Angular: Option to disable angular support and isolate angular dependencies (#45421)

* Angular: Initial setting that disables angular, load angular support in separate chunk

* Load angular panels on demand

* Load alerting in separate chunk only when angularSupportEnabled

* progress, do not export core_module if angular disabled

* Progress

* Update public/app/features/plugins/built_in_plugins.ts

Co-authored-by: Ryan McKinley <ryantxu@gmail.com>

* Removing remaining usage of angular from outside angular app (not counting plugins)

* Update config and docs

* Fix sample.ini

* Update public/app/features/alerting/AlertTab.tsx

Co-authored-by: Levente Balogh <balogh.levente.hu@gmail.com>

* Fixing prettier issue

Co-authored-by: Ryan McKinley <ryantxu@gmail.com>
Co-authored-by: Levente Balogh <balogh.levente.hu@gmail.com>

docs/sources/administration/configuration.md

@@ -582,6 +582,21 @@ Set Content Security Policy template used when adding the Content-Security-Polic
 
 <hr />
 
+### angular_support_enabled
+
+This currently defaults to `true` but will in Grafana v9 default to `false`. When set to false the angular framework and support components will not be loaded. This means that
+all plugins and core features that depend on angular support will stop working.
+
+Current core features that will stop working:
+
+- Heatmap panel
+- Old graph panel
+- Old table panel
+- Postgres, MySQL and MSSQL data source query editors
+- Legacy alerting edit rule UI
+
+Before we disable angular support by default we plan to migrate these remaining areas to React.
+
 ## [snapshots]
 
 ### external_enabled