PLT-4403 Add server-based channel autocomplete, search and paging (#4585)

* Add more channel paging API

* Add channel paging support to client

* Add DB channel search functions

* Add API for searching more channels

* Add more channel search functionality to client

* Add API for autocompleting channels

* Add channel autocomplete functionality to the client

* Move to be deprecated APIs to their own file

* Final clean-up

* Fixes related to feedback

* Localization changes

* Add unit as suffix to timeout constants

i18n/en.json

@@ -4035,6 +4035,10 @@
     "id": "store.sql_channel.analytics_type_count.app_error",
     "translation": "We couldn't get channel type counts"
   },
+  {
+    "id": "store.sql_channel.search.app_error",
+    "translation": "We encountered an error searching channels"
+  },
   {
     "id": "store.sql_channel.check_open_channel_permissions.app_error",
     "translation": "We couldn't check the permissions"