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)

db/migrate/20250523024825_remove_uuid_from_copilot_threads.rb

@@ -0,0 +1,8 @@
+class RemoveUuidFromCopilotThreads < ActiveRecord::Migration[7.1]
+  def change
+    remove_column :copilot_threads, :uuid, :string
+
+    add_column :copilot_threads, :assistant_id, :integer
+    add_index :copilot_threads, :assistant_id
+  end
+end

db/migrate/20250523024826_remove_user_id_from_copilot_messages.rb

@@ -0,0 +1,5 @@
+class RemoveUserIdFromCopilotMessages < ActiveRecord::Migration[7.1]
+  def change
+    remove_reference :copilot_messages, :user, index: true
+  end
+end

db/migrate/20250523031839_change_message_type_to_integer_in_copilot_messages.rb

@@ -0,0 +1,11 @@
+class ChangeMessageTypeToIntegerInCopilotMessages < ActiveRecord::Migration[7.1]
+  def up
+    remove_column :copilot_messages, :message_type
+    add_column :copilot_messages, :message_type, :integer, default: 0
+  end
+
+  def down
+    remove_column :copilot_messages, :message_type
+    add_column :copilot_messages, :message_type, :string, default: 'user'
+  end
+end