FEATURE: granular webhooks (#23070)

Before this change, webhooks could be only configured for specific groups like for example, all topic events.

We would like to have more granular control like for example topic_created or topic_destroyed.

Test are failing because plugins changed has to be merged as well:
discourse/discourse-assign#498
discourse/discourse-solved#248
discourse/discourse-topic-voting#159

plugins/chat/lib/chat/outgoing_web_hook_extension.rb

@@ -4,7 +4,7 @@ module Chat
   module OutgoingWebHookExtension
     def self.prepended(base)
       def base.enqueue_chat_message_hooks(event, payload, opts = {})
-        if active_web_hooks("chat_message").exists?
+        if active_web_hooks(event).exists?
           WebHook.enqueue_hooks(:chat_message, event, payload: payload, **opts)
         end
       end