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)

spec/factories/captain/copilot_thread.rb

@@ -3,6 +3,6 @@ FactoryBot.define do
     account
     user
     title { Faker::Lorem.sentence }
-    uuid { SecureRandom.uuid }
+    assistant { create(:captain_assistant, account: account) }
   end
 end