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)

config/routes.rb

@@ -60,8 +60,8 @@ Rails.application.routes.draw do
             end
             resources :assistant_responses
             resources :bulk_actions, only: [:create]
-            resources :copilot_threads, only: [:index] do
-              resources :copilot_messages, only: [:index]
+            resources :copilot_threads, only: [:index, :create] do
+              resources :copilot_messages, only: [:index, :create]
             end
             resources :documents, only: [:index, :show, :create, :destroy]
           end