Added support for S3 storage classes (#28319)

* Added support for S3 storage classes

* Added missing translations for S3 storage class

* Changed default storage class values to preserve original behaviour

* Changed storage class description and example

* Fix translations ordering

* Change configuration defaults to empty strings

* Remove redundant empty string check

* Validate storage class variable against constants from S3 API docs

* Validate export storage class against constants

* Use slices for config validation

* Applied patch for translation ordering

server/i18n/en.json

@@ -9157,6 +9157,10 @@
     "id": "model.config.is_valid.sql_query_timeout.app_error",
     "translation": "Invalid query timeout for SQL settings. Must be a positive number."
   },
+  {
+    "id": "model.config.is_valid.storage_class.app_error",
+    "translation": "Invalid storage class {{.Value}}."
+  },
   {
     "id": "model.config.is_valid.teammate_name_display.app_error",
     "translation": "Invalid teammate display. Must be 'full_name', 'nickname_full_name' or 'username'."