MM-10140: API Implementation for Schemes related Endpoints (#8615)

* Implement basic scheme CRUD endpoints.

* Get All Schemes (Paged) Endpoint and store plumbing.

* Add get teams/channels for schemes.

* Fix unit tests.

* Review fixes.

* More review fixes.

i18n/en.json

@@ -6654,6 +6654,14 @@
     "id": "store.sql_reaction.delete.save.app_error",
     "translation": "Unable to delete reaction"
   },
+  {
+    "id": "api.scheme.get_teams_for_scheme.scope.error",
+    "translation": "Unable to get the teams for scheme because the supplied scheme is not a team scheme."
+  },
+  {
+    "id": "api.scheme.get_channels_for_scheme.scope.error",
+    "translation": "Unable to get the channels for scheme because the supplied scheme is not a channel scheme."
+  },
   {
     "id": "store.sql_reaction.delete_all_with_emoj_name.delete_reactions.app_error",
     "translation": "Unable to delete reactions with the given emoji name"