DEV: Unhide chat experimental threads site setting (#22426)

This is in preparation for the V1 thread announcement,
where we will begin to allow site admins to enable this
themselves.

plugins/chat/config/locales/server.en.yml

@@ -20,6 +20,7 @@ en:
     max_mentions_per_chat_message: "Maximum number of @name notifications a user can use in a chat message."
     chat_max_direct_message_users: "Users cannot add more than this number of other users when creating a new direct message. Set to 0 to only allow messages to oneself. Staff are exempt from this setting."
     chat_allow_archiving_channels: "Allow staff to archive messages to a topic when closing a channel."
+    enable_experimental_chat_threaded_discussions: "EXPERIMENTAL: Allow staff to enable threading on chat channels, which allows for parallel discussions to occur in a channel when users reply to one another."
     errors:
       chat_default_channel: "The default chat channel must be a public channel."
       direct_message_enabled_groups_invalid: "You must specify at least one group for this setting. If you do not want anyone except staff to send direct messages, choose the staff group."

plugins/chat/config/settings.yml

@@ -115,5 +115,4 @@ chat:
     hidden: true
   enable_experimental_chat_threaded_discussions:
     default: false
-    hidden: true
     client: true