[8.9] [APM] Documentation updates (#160951) (#161036)

# Backport

This will backport the following commits from `main` to `8.9`:
- [[APM] Documentation updates
(#160951)](https://github.com/elastic/kibana/pull/160951)

<!--- Backport version: 8.9.7 -->

### Questions ?
Please refer to the [Backport tool
documentation](https://github.com/sqren/backport)

<!--BACKPORT [{"author":{"name":"Brandon
Morelli","email":"brandon.morelli@elastic.co"},"sourceCommit":{"committedDate":"2023-06-30T18:49:43Z","message":"[APM]
Documentation updates (#160951)\n\n### Summary\r\n\r\nThis PR makes a
handful of updates to the APM app documentation:\r\n\r\n- [x] **Agent
explorer**\r\n- New
page\r\n[here](https://kibana_160951.docs-preview.app.elstc.co/guide/en/kibana/master/agent-explorer.html).\r\n
- _Closes
https://github.com/elastic/observability-docs/issues/2886_\r\n- [x]
**Trace explorer**\r\n- New
section\r\n[here](https://kibana_160951.docs-preview.app.elstc.co/guide/en/kibana/master/traces.html#trace-explorer).\r\n
- _Closes
https://github.com/elastic/observability-docs/issues/2885_\r\n- [x]
**Dependency operations**\r\n- New
section\r\n[here](https://kibana_160951.docs-preview.app.elstc.co/guide/en/kibana/master/dependencies.html#dependencies-operations).\r\n
- _Closes
https://github.com/elastic/observability-docs/issues/2889_\r\n- [x]
**Adds missing settings and APM Labs info**\r\n- We didn't have
documentation on how to enable APM Labs. We
[do\r\nnow](https://kibana_160951.docs-preview.app.elstc.co/guide/en/kibana/master/apm-settings-in-kibana.html#apm-labs).\r\n-
I noticed Labs settings were missing from the documentation.
Those\r\nhave now been added to the [Kibana
advanced\r\nsettings](https://kibana_160951.docs-preview.app.elstc.co/guide/en/kibana/master/advanced-options.html#observability-advanced-settings).","sha":"9efbd2243cfd4fe9db98cb610f997ae46113cff3","branchLabelMapping":{"^v8.10.0$":"main","^v(\\d+).(\\d+).\\d+$":"$1.$2"}},"sourcePullRequest":{"labels":["Team:APM","release_note:skip","v8.9.0","v8.8.2","v8.10.0"],"number":160951,"url":"https://github.com/elastic/kibana/pull/160951","mergeCommit":{"message":"[APM]
Documentation updates (#160951)\n\n### Summary\r\n\r\nThis PR makes a
handful of updates to the APM app documentation:\r\n\r\n- [x] **Agent
explorer**\r\n- New
page\r\n[here](https://kibana_160951.docs-preview.app.elstc.co/guide/en/kibana/master/agent-explorer.html).\r\n
- _Closes
https://github.com/elastic/observability-docs/issues/2886_\r\n- [x]
**Trace explorer**\r\n- New
section\r\n[here](https://kibana_160951.docs-preview.app.elstc.co/guide/en/kibana/master/traces.html#trace-explorer).\r\n
- _Closes
https://github.com/elastic/observability-docs/issues/2885_\r\n- [x]
**Dependency operations**\r\n- New
section\r\n[here](https://kibana_160951.docs-preview.app.elstc.co/guide/en/kibana/master/dependencies.html#dependencies-operations).\r\n
- _Closes
https://github.com/elastic/observability-docs/issues/2889_\r\n- [x]
**Adds missing settings and APM Labs info**\r\n- We didn't have
documentation on how to enable APM Labs. We
[do\r\nnow](https://kibana_160951.docs-preview.app.elstc.co/guide/en/kibana/master/apm-settings-in-kibana.html#apm-labs).\r\n-
I noticed Labs settings were missing from the documentation.
Those\r\nhave now been added to the [Kibana
advanced\r\nsettings](https://kibana_160951.docs-preview.app.elstc.co/guide/en/kibana/master/advanced-options.html#observability-advanced-settings).","sha":"9efbd2243cfd4fe9db98cb610f997ae46113cff3"}},"sourceBranch":"main","suggestedTargetBranches":["8.9","8.8"],"targetPullRequestStates":[{"branch":"8.9","label":"v8.9.0","labelRegex":"^v(\\d+).(\\d+).\\d+$","isSourceBranch":false,"state":"NOT_CREATED"},{"branch":"8.8","label":"v8.8.2","labelRegex":"^v(\\d+).(\\d+).\\d+$","isSourceBranch":false,"state":"NOT_CREATED"},{"branch":"main","label":"v8.10.0","labelRegex":"^v8.10.0$","isSourceBranch":true,"state":"MERGED","url":"https://github.com/elastic/kibana/pull/160951","number":160951,"mergeCommit":{"message":"[APM]
Documentation updates (#160951)\n\n### Summary\r\n\r\nThis PR makes a
handful of updates to the APM app documentation:\r\n\r\n- [x] **Agent
explorer**\r\n- New
page\r\n[here](https://kibana_160951.docs-preview.app.elstc.co/guide/en/kibana/master/agent-explorer.html).\r\n
- _Closes
https://github.com/elastic/observability-docs/issues/2886_\r\n- [x]
**Trace explorer**\r\n- New
section\r\n[here](https://kibana_160951.docs-preview.app.elstc.co/guide/en/kibana/master/traces.html#trace-explorer).\r\n
- _Closes
https://github.com/elastic/observability-docs/issues/2885_\r\n- [x]
**Dependency operations**\r\n- New
section\r\n[here](https://kibana_160951.docs-preview.app.elstc.co/guide/en/kibana/master/dependencies.html#dependencies-operations).\r\n
- _Closes
https://github.com/elastic/observability-docs/issues/2889_\r\n- [x]
**Adds missing settings and APM Labs info**\r\n- We didn't have
documentation on how to enable APM Labs. We
[do\r\nnow](https://kibana_160951.docs-preview.app.elstc.co/guide/en/kibana/master/apm-settings-in-kibana.html#apm-labs).\r\n-
I noticed Labs settings were missing from the documentation.
Those\r\nhave now been added to the [Kibana
advanced\r\nsettings](https://kibana_160951.docs-preview.app.elstc.co/guide/en/kibana/master/advanced-options.html#observability-advanced-settings).","sha":"9efbd2243cfd4fe9db98cb610f997ae46113cff3"}}]}]
BACKPORT-->

Co-authored-by: Brandon Morelli <brandon.morelli@elastic.co>

docs/apm/agent-explorer.asciidoc

@@ -0,0 +1,18 @@
+[[agent-explorer]]
+=== APM Agent explorer
+
+++++
+<titleabbrev>Identify deployment details for APM agents</titleabbrev>
+++++
+
+beta::[]
+
+APM agent explorer provides a centralized panel to identify APM agent deployment details, like service name, environment, instances, and agent name, version, and documentation.
+
+[role="screenshot"]
+image::apm/images/apm-agent-explorer.png[APM agent explorer]
+
+Select an APM agent to expand it and view the details of each agent instance.
+
+[role="screenshot"]
+image::apm/images/apm-agent-explorer-flyout.png[APM agent explorer flyout]

docs/apm/dependencies.asciidoc

@@ -30,3 +30,19 @@ If your usage pattern _has_ changed, the dependency view can quickly show you wh
 that pattern change exists in all upstream services, or just a subset of your services.
 You might then start digging into traces coming from
 impacted services to determine why that pattern change has occurred.
+
+[float]
+[[dependencies-operations]]
+==== Operations
+
+beta::[]
+
+**Dependency operations** provides a granular breakdown of the operations/queries a dependency is executing.
+
+[role="screenshot"]
+image::apm/images/operations.png[operations view in the APM app in Kibana]
+
+Selecting an operation displays the operation's impact and performance trends over time, via key metrics like latency, throughput, and failed transaction rate. In addition, the <<spans,**Trace sample timeline**>> provides a visual drill-down into an end-to-end trace sample.
+
+[role="screenshot"]
+image::apm/images/operations-detail.png[operations detail view in the APM app in Kibana]

docs/apm/how-to-guides.asciidoc

@@ -11,6 +11,7 @@ Learn how to perform common APM app tasks.
 * <<custom-links>>
 * <<filters>>
 * <<correlations>>
+* <<agent-explorer>>
 * <<machine-learning-integration>>
 * <<apm-lambda>>
 * <<advanced-queries>>
@@ -30,6 +31,8 @@ include::filters.asciidoc[]
 
 include::correlations.asciidoc[]
 
+include::agent-explorer.asciidoc[]
+
 include::machine-learning.asciidoc[]
 
 include::lambda.asciidoc[]

docs/apm/settings.asciidoc

@@ -21,3 +21,14 @@ include::./../settings/apm-settings.asciidoc[tag=apm-indices-settings]
 === General APM settings
 
 include::./../settings/apm-settings.asciidoc[tag=general-apm-settings]
+
+[float]
+[[apm-labs]]
+=== APM Labs
+
+**APM Labs** allows you to easily try out new features that are technical preview.
+
+To enable APM labs, navigate to **APM** > **Settings** > **General settings** and toggle **Enable labs button in APM**.
+Select **Save changes** and refresh the page.
+
+After enabling **APM Labs** select **Labs** in the toolbar to see the technical preview features available to try out.

docs/apm/traces.asciidoc

@@ -19,3 +19,18 @@ If there's a particular endpoint you're worried about, select it to view its
 
 [role="screenshot"]
 image::apm/images/apm-traces.png[Example view of the Traces overview in APM app in Kibana]
+
+[float]
+[[trace-explorer]]
+==== Trace explorer
+
+preview::[]
+
+**Trace explorer** is an experimental top-level search tool that allows you to query your traces using <<kuery-query,Kibana Query Language (KQL)>> or {ref}/eql.html[Event Query Language (EQL)].
+
+Curate your own custom queries, or use the <<service-maps,**Service map**>> to find and select edges to automatically generate queries based on your selection:
+
+[role="screenshot"]
+image::apm/images/trace-explorer.png[Trace explorer]
+
+Enable **Trace explorer** in <<apm-labs,APM Labs>> or in <<observability-apm-trace-explorer-tab,{kib} advanced settings>>.

docs/management/advanced-options.asciidoc

@@ -393,9 +393,20 @@ value is 10000.
 [[apm-enable-service-overview]]`apm:enableServiceOverview`::
 When enabled, displays the *Overview* tab for services in *APM*.
 
+[[observability-apm-critical-path]]`observability:apmEnableCriticalPath`::
+When enabled, displays the critical path of a trace.
+
+[[observability-enable-progressive-loading]]`observability:apmProgressiveLoading`::
+preview:[] When enabled, uses progressive loading of some APM views.
+Data may be requested with a lower sampling rate first, with lower accuracy but faster response times,
+while the unsampled data loads in the background.
+
 [[observability-apm-optimized-sort]]`observability:apmServiceInventoryOptimizedSorting`::
 preview:[] Sorts services without anomaly detection rules on the APM Service inventory page by service name.
 
+[[observability-enable-aws-lambda-metrics]]`observability:enableAwsLambdaMetrics`::
+preview:[] Display Amazon Lambda metrics in the service metrics tab.
+
 [[observability-apm-enable-comparison]]`observability:enableComparisonByDefault`::
 Enables the comparison feature in the APM app.
 
@@ -408,6 +419,9 @@ When enabled, allows you to inspect {es} queries in API responses.
 [[observability-apm-enable-service-groups]]`observability:enableServiceGroups`::
 preview:[] When enabled, allows users to create Service Groups from the APM Service Inventory page.
 
+[[observability-apm-trace-explorer-tab]]`observability:apmTraceExplorerTab`::
+preview:[] Enable the APM Trace Explorer feature, that allows you to search and inspect traces with KQL or EQL.
+
 [float]
 [[kibana-reporting-settings]]
 ==== Reporting