feat: Add support for realtime-events in copilot-threads and copilot-messages (#11557)

- Add API support for creating a thread
- Add API support for creating a message
- Remove uuid from thread (no longer required, we will use existing
websocket connection to send messages)
- Update message_type to a column (user, assistant, assistant_thinking)

lib/events/types.rb

@@ -54,4 +54,7 @@ module Events::Types
   # agent events
   AGENT_ADDED = 'agent.added'
   AGENT_REMOVED = 'agent.removed'
+
+  # copilot events
+  COPILOT_MESSAGE_CREATED = 'copilot.message.created'
 end