[docs] Convert migration guide to asciidoc (#82600)

* Initial conversion to asciidoc

* Update and split migration guide

* Convert MIGRATION_EXAMPLES to asciidoc

* build with --focus flag

* convert migration guide to asciidoc

* cleanup migration_examples

* fix wrong Heading size

* update links in docs

* Apply suggestions from code review

Co-authored-by: Rudolf Meijering <skaapgif@gmail.com>

* Apply suggestions from code review

Co-authored-by: Rudolf Meijering <skaapgif@gmail.com>

* add tooling section

* explain purpose of each lifecycle method

* cleanup docs

* cleanup p2

* fix wrong link

* resturcture core docs

* fix wrong link

* update missing links

* Apply suggestions from code review

Co-authored-by: gchaps <33642766+gchaps@users.noreply.github.com>

* address comments

* add a commenta about plugin-helpers preconfigured

* improve density of tables

* fix lik

* remove links to the migration guide

* address comments

* Apply suggestions from code review

Co-authored-by: gchaps <33642766+gchaps@users.noreply.github.com>

* address @gchaps comments

* Apply suggestions from code review

Co-authored-by: gchaps <33642766+gchaps@users.noreply.github.com>

* change format of ES client change list

Co-authored-by: Josh Dover <me@joshdover.com>
Co-authored-by: Rudolf Meijering <skaapgif@gmail.com>
Co-authored-by: gchaps <33642766+gchaps@users.noreply.github.com>

docs/developer/contributing/development-ci-metrics.asciidoc

@@ -75,7 +75,7 @@ In order to prevent the page load bundles from growing unexpectedly large we lim
 
 In most cases the limit should be high enough that PRs shouldn't trigger overages, but when they do make sure it's clear what is cuasing the overage by trying the following:
 
-1. Run the optimizer locally with the `--profile` flag to produce webpack `stats.json` files for bundles which can be inspected using a number of different online tools. Focus on the chunk named `{pluginId}.plugin.js`; the `*.chunk.js` chunks make up the `async chunks size` metric which is currently unlimited and is the main way that we {kib-repo}blob/{branch}/src/core/MIGRATION.md#keep-kibana-fast[reduce the size of page load chunks].
+1. Run the optimizer locally with the `--profile` flag to produce webpack `stats.json` files for bundles which can be inspected using a number of different online tools. Focus on the chunk named `{pluginId}.plugin.js`; the `*.chunk.js` chunks make up the `async chunks size` metric which is currently unlimited and is the main way that we <<plugin-performance, reduce the size of page load chunks>>.
 +
 [source,shell]
 -----------
@@ -111,7 +111,7 @@ prettier -w {pluginDir}/target/public/{pluginId}.plugin.js
 
 6. If all else fails reach out to Operations for help.
 
-Once you've identified the files which were added to the build you likely just need to stick them behind an async import as described in {kib-repo}blob/{branch}/src/core/MIGRATION.md#keep-kibana-fast[the MIGRATION.md docs].
+Once you've identified the files which were added to the build you likely just need to stick them behind an async import as described in <<plugin-performance, Plugin performance>>.
 
 In the case that the bundle size is not being bloated by anything obvious, but it's still larger than the limit, you can raise the limit in your PR. Do this either by editting the {kib-repo}blob/{branch}/packages/kbn-optimizer/limits.yml[`limits.yml` file] manually or by running the following to have the limit updated to the current size + 15kb