DEV: the ability to define setting areas (#28570)

A new setting attribute is used to define the areas (separated by `|`).

In addition, endpoint `/admin/config/site_settings.json` accepts new `filter_area` data.

plugins/chat/config/settings.yml

@@ -53,6 +53,7 @@ chat:
   chat_auto_silence_from_flags_duration:
     default: 60
     min: 0
+    area: "flags"
   chat_allow_archiving_channels:
     default: false
     client: true
@@ -106,6 +107,7 @@ chat:
     type: group_list
     allow_any: false
     refresh: true
+    area: "flags"
   max_mentions_per_chat_message:
     client: true
     type: integer