feat: Add support for persistent copilot threads and messages (#11489)

The agents can see the previous conversations with the copilot if needed
with this change. We would have to cleanup the data after a while. For
now, that is not considered.

This PR adds:
- A new model for copilot_threads (intentionally named thread instead of
conversation to avoid confusion), copilot_messages
- Add the controller to fetch previous threads and messages.

spec/factories/captain/copilot_thread.rb

@@ -0,0 +1,8 @@
+FactoryBot.define do
+  factory :captain_copilot_thread, class: 'CopilotThread' do
+    account
+    user
+    title { Faker::Lorem.sentence }
+    uuid { SecureRandom.uuid }
+  end
+end