[docs] Convert migration guide to asciidoc (#82600) (#84181)

* 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>
# Conflicts:
#	docs/developer/architecture/core/saved-objects-service.asciidoc
#	docs/developer/architecture/index.asciidoc
#	src/core/MIGRATION.md
#	src/core/README.md

docs/developer/architecture/add-data-tutorials.asciidoc

@@ -28,11 +28,11 @@ Then register the tutorial object by calling `home.tutorials.registerTutorial(tu
 String values can contain variables that are substituted when rendered. Variables are specified by `{}`.
 For example: `{config.docs.version}` is rendered as `6.2` when running the tutorial in {kib} 6.2.
 
-link:{kib-repo}tree/{branch}/src/legacy/core_plugins/kibana/public/home/np_ready/components/tutorial/replace_template_strings.js#L23[Provided variables]
+link:{kib-repo}tree/{branch}/src/plugins/home/public/application/components/tutorial/replace_template_strings.js[Provided variables]
 
 [discrete]
 ==== Markdown
 String values can contain limited Markdown syntax.
 
-link:{kib-repo}tree/{branch}/src/legacy/core_plugins/kibana/public/home/components/tutorial/content.js#L8[Enabled Markdown grammars]
+link:{kib-repo}tree/{branch}/src/legacy/core_plugins/kibana/public/home/components/tutorial/content.js[Enabled Markdown grammars]