[DOCS] Organize breaking changes by component (#79162)

* Reorganizes the 8.0.0 and 8.1.0 breaking changes and deprecations into component-based categories.
* Adds an ESS icon to cluster settings on the ESS user settings allowlist.
* Adds tips for sections that aren't relevant to Cloud users.
* Updates the labels for some items to provide better context.

Co-authored-by: debadair <debadair@elastic.co>

docs/reference/migration/index.asciidoc

@@ -1,8 +1,9 @@
 [[breaking-changes]]
 = Migration guide
 
-[partintro]
---
+:ess-setting-change: {ess-icon} indicates a change to a supported {cloud}/ec-add-user-settings.html[user setting] for {ess}.
+:ess-skip-section: If you use {ess}, skip this section. {ess} handles these changes for you.
+
 This section discusses the changes that you need to be aware of to migrate
 your application to {version}. For more information about what's new in this
 release, see the <<release-highlights>> and <<es-release-notes>>.
@@ -38,6 +39,5 @@ For information about how to upgrade your cluster, see <<setup-upgrade>>.
 * <<migrating-8.1,Migrating to 8.1>>
 * <<migrating-8.0,Migrating to 8.0>>
 
---
 include::migrate_8_1.asciidoc[]
 include::migrate_8_0.asciidoc[]

docs/reference/migration/migrate_8_0.asciidoc

@@ -9,38 +9,7 @@ your application to {es} 8.0.
 
 See also <<release-highlights>> and <<es-release-notes>>.
 
-coming[8.0.0]
-
-* <<breaking_80_aggregations_changes>>
-* <<breaking_80_allocation_changes>>
-* <<breaking_80_analysis_changes>>
-* <<breaking_80_breaker_changes>>
-* <<breaking_80_cluster_changes>>
-* <<breaking_80_ccr_changes>>
-* <<breaking_80_discovery_changes>>
-* <<breaking_80_eql_changes>>
-* <<breaking_80_http_changes>>
-* <<breaking_80_ilm_changes>>
-* <<breaking_80_indices_changes>>
-* <<breaking_80_ingest_changes>>
-* <<breaking_80_java_changes>>
-* <<breaking_80_logging_changes>>
-* <<breaking_80_mappings_changes>>
-* <<breaking_80_network_changes>>
-* <<breaking_80_node_changes>>
-* <<breaking_80_packaging_changes>>
-* <<breaking_80_reindex_changes>>
-* <<breaking_80_api_changes>>
-* <<breaking_80_rollup_changes>>
-* <<breaking_80_scripting_changes>>
-* <<breaking_80_search_changes>>
-* <<breaking_80_security_changes>>
-* <<breaking_80_settings_changes>>
-* <<breaking_80_snapshots_changes>>
-* <<breaking_80_threadpool_changes>>
-* <<breaking_80_transform_changes>>
-* <<breaking_80_transport_changes>>
-* <<breaking_80_watcher_changes>>
+coming::[8.0.0]
 
 [discrete]
 [[breaking-changes-8.0]]
@@ -58,93 +27,18 @@ the old behavior is supported until the next major release.
 To find out if you are using any deprecated functionality,
 enable <<deprecation-logging, deprecation logging>>.
 
-//NOTE: The notable-breaking-changes tagged regions are re-used in the
-//Installation and Upgrade Guide
-
-//tag::notable-breaking-changes[]
-
-.Indices created in {es} 6.x and earlier versions are not supported.
-[%collapsible]
-====
-*Details* +
-Elasticsearch 8.0 can read indices created in version 7.0 or above. An
-Elasticsearch 8.0 node will not start in the presence of indices created in a
-version of Elasticsearch before 7.0.
-
-*Impact* +
-Reindex indices created in {es} 6.x or before with {es} 7.x if they need to be carried forward to  {es} 8.x.
-====
-
-.REST API endpoints containing `_xpack` have been removed.
-[%collapsible]
-====
-*Details* +
-In 7.0, we deprecated REST endpoints that contain `_xpack` in their path. These
-endpoints are now removed in 8.0. Each endpoint that was deprecated and removed
-is replaced with a new endpoint that does not contain `_xpack`. As an example,
-`/{index}/_xpack/graph/_explore` is replaced by `/{index}/_graph/explore`.
-
-*Impact* +
-Use the replacement REST API endpoints. Requests submitted to the `_xpack`
-API endpoints will return an error.
-====
-
-.Several EOL operating systems are no longer supported.
-[%collapsible]
-====
-*Details* +
-The following operating systems have reached their end of life and are no longer
-supported by {es}:
-
-* Amazon Linux
-* CentOS 6
-* Debian 8
-* openSUSE Leap 42
-* Oracle Enterprise Linux 6
-* Ubuntu 16.04
-
-We've also removed support for `SysV init`. No supported operating systems use
-the `SysV init` process.
-
-*Details* +
-Ensure your nodes use a
-https://www.elastic.co/support/matrix#matrix_os[supported operating system].
-Running {es} on an unsupported operating system can result in unexpected errors
-or failures.
-====
-
-// end::notable-breaking-changes[]
-
-include::migrate_8_0/aggregations.asciidoc[]
-include::migrate_8_0/allocation.asciidoc[]
-include::migrate_8_0/analysis.asciidoc[]
-include::migrate_8_0/breaker.asciidoc[]
-include::migrate_8_0/cluster.asciidoc[]
-include::migrate_8_0/ccr.asciidoc[]
-include::migrate_8_0/discovery.asciidoc[]
-include::migrate_8_0/eql.asciidoc[]
-include::migrate_8_0/http.asciidoc[]
-include::migrate_8_0/ilm.asciidoc[]
-include::migrate_8_0/indices.asciidoc[]
-include::migrate_8_0/ingest.asciidoc[]
-include::migrate_8_0/java.asciidoc[]
-include::migrate_8_0/logging.asciidoc[]
-include::migrate_8_0/mappings.asciidoc[]
-include::migrate_8_0/network.asciidoc[]
-include::migrate_8_0/node.asciidoc[]
-include::migrate_8_0/packaging.asciidoc[]
-include::migrate_8_0/reindex.asciidoc[]
-include::migrate_8_0/api.asciidoc[]
-include::migrate_8_0/rollup.asciidoc[]
-include::migrate_8_0/scripting.asciidoc[]
-include::migrate_8_0/search.asciidoc[]
-include::migrate_8_0/security.asciidoc[]
-include::migrate_8_0/settings.asciidoc[]
-include::migrate_8_0/snapshots.asciidoc[]
-include::migrate_8_0/threadpool.asciidoc[]
+include::migrate_8_0/_cluster-node-setting-changes.asciidoc[]
+include::migrate_8_0/_command-line-tool-changes.asciidoc[]
+include::migrate_8_0/_index-setting-changes.asciidoc[]
+include::migrate_8_0/_java-api-changes.asciidoc[]
+include::migrate_8_0/_jvm-option-changes.asciidoc[]
+include::migrate_8_0/_logging-changes.asciidoc[]
+include::migrate_8_0/_mapping-changes.asciidoc[]
+include::migrate_8_0/_packaging-changes.asciidoc[]
+include::migrate_8_0/_painless-changes.asciidoc[]
+include::migrate_8_0/_rest-api-changes.asciidoc[]
+include::migrate_8_0/_system-req-changes.asciidoc[]
 include::migrate_8_0/transform.asciidoc[]
-include::migrate_8_0/transport.asciidoc[]
-include::migrate_8_0/watcher.asciidoc[]
 
 [discrete]
 [[deprecated-8.0]]
@@ -161,9 +55,12 @@ the old behavior is supported until the next major release.
 To find out if you are using any deprecated functionality,
 enable <<deprecation-logging, deprecation logging>>.
 
+//NOTE: The notable-breaking-changes tagged regions are re-used in the
+//Installation and Upgrade Guide
+//tag::notable-breaking-changes[]
 [discrete]
-[[breaking_80_settings_deprecations]]
-==== Settings deprecations
+[[breaking_80_cluster_node_setting_deprecations]]
+==== Cluster and node setting deprecations
 
 [[deprecate-transient-cluster-settings]]
 .Transient cluster settings are deprecated.
@@ -183,6 +80,31 @@ settings instead. See the
 {ref}/transient-settings-migration-guide.html[Transient settings migration
 guide]. 
 ====
+//end::notable-breaking-changes[]
+
+[discrete]
+[[breaking_80_command_line_tool_deprecations]]
+==== Command line tool deprecations
+
+TIP: {ess-skip-section}
+
+[[deprecate-elasticsearch-setup-passwords]]
+.The `elasticsearch-setup-passwords` tool is deprecated.
+[%collapsible]
+====
+*Details* +
+The `elasticsearch-setup-passwords` tool is deprecated in 8.0. To
+manually reset the password for built-in users (including the `elastic` user), use
+the {ref}/reset-password.html[`elasticsearch-reset-password`] tool, the {es}
+{ref}/security-api-change-password.html[change passwords API], or the
+User Management features in {kib}. 
+`elasticsearch-setup-passwords` will be removed in a future release.
+
+*Impact* +
+Passwords are generated automatically for the `elastic` user when you start {es} for the first time. If you run `elasticsearch-setup-passwords` after
+starting {es}, it will fail because the `elastic`
+user password is already configured.
+====
 
 include::migrate_8_0/migrate_to_java_time.asciidoc[]
 include::transient-settings-migration-guide.asciidoc[]