[DOCS] Overhaul snapshot and restore docs (#79081)

Makes several changes to consolidate snapshot and backup-related docs.

Highlights:

* Adds info about supported ESS snapshot repository types
* Adds docs for Kibana's Snapshot and Restore feature
* Combines tutorial pages related to taking and managing snapshots
* Consolidates explanations of the snapshot process
* Incorporates SLM into the snapshot tutorial
* Removes duplicate "back up a cluster" pages

docs/reference/slm/apis/slm-api.asciidoc

@@ -3,8 +3,9 @@
 == {slm-cap} APIs
 
 You use the following APIs to set up policies to automatically take snapshots and 
-control how long they are retained. 
-For more information about {slm} ({slm-init}), see <<snapshot-lifecycle-management>>.
+control how long they are retained.
+
+For more information about {slm} ({slm-init}), see <<automate-snapshots-slm>>.
 
 [discrete]
 [[slm-api-policy-endpoint]]

docs/reference/slm/apis/slm-execute.asciidoc

@@ -58,7 +58,7 @@ If successful, this request returns the generated snapshot name:
 
 The snapshot is taken in the background. You can use the 
 <<snapshot-lifecycle-management-api,snapshot APIs>> to 
-<<snapshots-monitor-snapshot-restore,monitor the status of the snapshot>>.
+<<monitor-snapshot,monitor the status of the snapshot>>.
 
 To see the status of a policy's most recent snapshot, you can use the 
 <<slm-api-get-policy,get snapshot lifecycle policy API>>.

docs/reference/slm/apis/slm-get.asciidoc

@@ -11,9 +11,9 @@ information about the latest snapshot attempts.
 [[slm-api-get-request]]
 ==== {api-request-title}
 
-`GET /_slm/policy/<policy-id>`
+`GET _slm/policy/<policy-id>`
 
-`GET /_slm/policy`
+`GET _slm/policy`
 
 [[slm-api-get-lifecycle-prereqs]]
 ==== {api-prereq-title}
@@ -44,44 +44,44 @@ Comma-separated list of snapshot lifecycle policy IDs.
 
 ////
 [source,console]
---------------------------------------------------
-PUT /_slm/policy/daily-snapshots
+----
+PUT _slm/policy/daily-snapshots
 {
-  "schedule": "0 30 1 * * ?", <1>
-  "name": "<daily-snap-{now/d}>", <2>
-  "repository": "my_repository", <3>
-  "config": { <4>
-    "indices": ["data-*", "important"], <5>
+  "schedule": "0 30 1 * * ?",
+  "name": "<daily-snap-{now/d}>",
+  "repository": "my_repository",
+  "config": {
+    "indices": ["data-*", "important"],
     "ignore_unavailable": false,
     "include_global_state": false
   },
-  "retention": { <6>
-    "expire_after": "30d", <7>
-    "min_count": 5, <8>
-    "max_count": 50 <9>
+  "retention": {
+    "expire_after": "30d",
+    "min_count": 5,
+    "max_count": 50
   }
 }
---------------------------------------------------
+----
 // TEST[setup:setup-repository]
 ////
 
 Get the `daily-snapshots` policy:
 
 [source,console]
---------------------------------------------------
-GET /_slm/policy/daily-snapshots?human
---------------------------------------------------
+----
+GET _slm/policy/daily-snapshots?human
+----
 // TEST[continued]
 
 This request returns the following response:
 
 [source,console-result]
---------------------------------------------------
+----
 {
-  "daily-snapshots" : {
-    "version": 1, <1>
-    "modified_date": "2019-04-23T01:30:00.000Z", <2>
-    "modified_date_millis": 1556048137314,
+  "daily-snapshots": {
+    "version": 1,                                 <1>
+    "modified_date": "2099-05-06T01:30:00.000Z",  <2>
+    "modified_date_millis": 4081757400000,
     "policy" : {
       "schedule": "0 30 1 * * ?",
       "name": "<daily-snap-{now/d}>",
@@ -104,12 +104,16 @@ This request returns the following response:
       "snapshots_deleted": 0,
       "snapshot_deletion_failures": 0
     },
-    "next_execution": "2019-04-24T01:30:00.000Z", <3>
-    "next_execution_millis": 1556048160000
+    "next_execution": "2099-05-07T01:30:00.000Z", <3>
+    "next_execution_millis": 4081843800000
   }
 }
---------------------------------------------------
-// TESTRESPONSE[s/"modified_date": "2019-04-23T01:30:00.000Z"/"modified_date": $body.daily-snapshots.modified_date/ s/"modified_date_millis": 1556048137314/"modified_date_millis": $body.daily-snapshots.modified_date_millis/ s/"next_execution": "2019-04-24T01:30:00.000Z"/"next_execution": $body.daily-snapshots.next_execution/ s/"next_execution_millis": 1556048160000/"next_execution_millis": $body.daily-snapshots.next_execution_millis/]
+----
+// TESTRESPONSE[s/"version": 1/"version": $body.daily-snapshots.version/]
+// TESTRESPONSE[s/"modified_date": "2099-05-06T01:30:00.000Z"/"modified_date": $body.daily-snapshots.modified_date/]
+// TESTRESPONSE[s/"modified_date_millis": 4081757400000/"modified_date_millis": $body.daily-snapshots.modified_date_millis/]
+// TESTRESPONSE[s/"next_execution": "2099-05-07T01:30:00.000Z"/"next_execution": $body.daily-snapshots.next_execution/]
+// TESTRESPONSE[s/"next_execution_millis": 4081843800000/"next_execution_millis": $body.daily-snapshots.next_execution_millis/]
 <1> The version of the snapshot policy, only the latest version is stored and incremented when the policy is updated
 <2> The last time this policy was modified.
 <3> The next time this policy will be executed.
@@ -119,7 +123,7 @@ This request returns the following response:
 ===== Get all policies
 
 [source,console]
---------------------------------------------------
-GET /_slm/policy
---------------------------------------------------
+----
+GET _slm/policy
+----
 // TEST[continued]

docs/reference/slm/apis/slm-put.asciidoc

@@ -15,9 +15,9 @@ Creates or updates a snapshot lifecycle policy.
 [[slm-api-put-prereqs]]
 ==== {api-prereq-title}
 
-If the {es} {security-features} are enabled, you must have the 
+If the {es} {security-features} are enabled, you must have the
 `manage_slm` cluster privilege and the `manage` index privilege
-for any included indices to use this API. 
+for any included indices to use this API.
 For more information, see <<security-privileges>>.
 
 [[slm-api-put-desc]]
@@ -63,13 +63,13 @@ include::{es-repo-dir}/snapshot-restore/apis/create-snapshot-api.asciidoc[tag=sn
 (Required, string)
 Name automatically assigned to each snapshot created by the policy.
 <<date-math-index-names,Date math>> is supported.
-To prevent conflicting snapshot names, a UUID is automatically appended to each 
+To prevent conflicting snapshot names, a UUID is automatically appended to each
 snapshot name.
 
 `repository`::
 (Required, string)
-Repository used to store snapshots created by this policy. This repository must 
-exist prior to the policy's creation. You can create a repository using the 
+Repository used to store snapshots created by this policy. This repository must
+exist prior to the policy's creation. You can create a repository using the
 <<modules-snapshots,snapshot repository API>>.
 
 [[slm-api-put-retention]]
@@ -86,6 +86,7 @@ Time period after which a snapshot is considered expired and eligible for
 deletion. {slm-init} deletes expired snapshots based on the
 <<slm-retention-schedule,`slm.retention_schedule`>>.
 
+// To update {max-snapshot-count}, see docs/Version.asciidoc
 `max_count`::
 (Optional, integer)
 Maximum number of snapshots to retain, even if the snapshots have not yet
@@ -94,9 +95,8 @@ policy retains the most recent snapshots and deletes older snapshots. This limit
 only includes snapshots with a <<get-snapshot-api-response-state,`state`>> of
 `SUCCESS`.
 +
-NOTE: The maximum number of snapshots in a repository should not exceed `200`. This ensures that the snapshot repository metadata does not
-grow to a size which might destabilize the master node. If the `max_count` setting is not set, this limit should be enforced by configuring
-other retention rules such that the repository size does not exceed `200` snapshots.
+NOTE: This value should not exceed {max-snapshot-count}. See
+<<snapshot-retention-limits>>.
 
 `min_count`::
 (Optional, integer)