Rebuild channel index (#26080)

* WIP

* Added rebuild channels index functionality

* Added rough logic to send message to all sysadmins

* WIP

* WIP

* WIP

* Cleanup

* i18n fix

* reading through all pages of system admins

* Fixed webapp style

* i18n fix

* Added help text

* i18n fix

* i18n update

* Updated system console button action

* Updated snapshots

* some cleanup

* Updated snapshot

* Update server/channels/app/server.go

Co-authored-by: Daniel Espino García <larkox@gmail.com>

* fixed typo

* Refactoring to improve readibility

* moved index check to API later during config update

* Added some docs

* Updated get system bot

---------

Co-authored-by: Daniel Espino García <larkox@gmail.com>

server/i18n/en.json

@@ -1649,6 +1649,10 @@
     "id": "api.config.reload_config.app_error",
     "translation": "Failed to reload config."
   },
+  {
+    "id": "api.config.update.elasticsearch.autocomplete_cannot_be_enabled_error",
+    "translation": "Channel autocomplete cannot be enabled as channel index schema is out of date. It is recommended to regenerate your channel index. See the Mattermost changelog for more information"
+  },
   {
     "id": "api.config.update_config.clear_siteurl.app_error",
     "translation": "Site URL cannot be cleared."
@@ -4754,6 +4758,10 @@
     "id": "app.channel.delete.app_error",
     "translation": "Unable to delete the channel."
   },
+  {
+    "id": "app.channel.elasticsearch_channel_index.notify_admin.message",
+    "translation": "Your Elasticsearch channel index schema is out of date. It is recommended to regenerate your channel index.\nClick the `Rebuild Channels Index` button in [Elasticsearch section in System Console]({{.ElasticsearchSection}}) to fix the issue.\nSee Mattermost changelog for more information."
+  },
   {
     "id": "app.channel.get.existing.app_error",
     "translation": "Unable to find the existing channel."
@@ -7462,6 +7470,10 @@
     "id": "bleveengine.purge_file_index.error",
     "translation": "Failed to purge file indexes."
   },
+  {
+    "id": "bleveengine.purge_list.not_implemented",
+    "translation": "Purge list feature is not available for Bleve."
+  },
   {
     "id": "bleveengine.purge_post_index.error",
     "translation": "Failed to purge post indexes."
@@ -7826,10 +7838,18 @@
     "id": "ent.elasticsearch.post.get_posts_batch_for_indexing.error",
     "translation": "Unable to get the posts batch for indexing."
   },
+  {
+    "id": "ent.elasticsearch.purge_index.delete_failed",
+    "translation": "Failed to delete an Elasticsearch index"
+  },
   {
     "id": "ent.elasticsearch.purge_indexes.delete_failed",
     "translation": "Failed to delete Elasticsearch index"
   },
+  {
+    "id": "ent.elasticsearch.purge_indexes.unknown_index",
+    "translation": "Failed to delete an unknown index specified"
+  },
   {
     "id": "ent.elasticsearch.refresh_indexes.refresh_failed",
     "translation": "Failed to refresh Elasticsearch indexes"