chore: API improvements (#3637)

- Unique validations for Inbox members and Team member objects
- Move notification processing to Async

app/dispatchers/async_dispatcher.rb

@@ -15,6 +15,7 @@ class AsyncDispatcher < BaseDispatcher
       EventListener.instance,
       HookListener.instance,
       InstallationWebhookListener.instance,
+      NotificationListener.instance,
       WebhookListener.instance
     ]
   end

app/dispatchers/sync_dispatcher.rb

@@ -5,6 +5,6 @@ class SyncDispatcher < BaseDispatcher
   end
 
   def listeners
-    [ActionCableListener.instance, AgentBotListener.instance, NotificationListener.instance]
+    [ActionCableListener.instance, AgentBotListener.instance]
   end
 end