Add support for subentries to config entries (#117355)

* Add support for subentries to config entries

* Improve error handling and test coverage

* Include subentry_id in subentry containers

* Auto-generate subentry_id and add optional unique_id

* Tweak

* Update tests

* Fix stale docstring

* Address review comments

* Typing tweaks

* Add methods to ConfigEntries to add and remove subentry

* Improve ConfigSubentryData typed dict

* Update test snapshots

* Adjust tests

* Fix unique_id logic

* Allow multiple subentries with None unique_id

* Add number of subentries to config entry JSON representation

* Add subentry translation support

* Allow integrations to implement multiple subentry flows

* Update translations schema

* Adjust exception text

* Change subentry flow init step to user

* Prevent creating a subentry with colliding unique_id

* Update tests

* Address review comments

* Remove duplicaetd unique_id collision check

* Remove change from the future

* Improve test coverage

* Add default value for unique_id

tests/components/fronius/snapshots/test_diagnostics.ambr

@@ -17,6 +17,8 @@
       'pref_disable_new_entities': False,
       'pref_disable_polling': False,
       'source': 'user',
+      'subentries': list([
+      ]),
       'title': 'Mock Title',
       'unique_id': '**REDACTED**',
       'version': 1,