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.

enterprise/app/controllers/api/v1/accounts/captain/copilot_messages_controller.rb

@@ -0,0 +1,25 @@
+class Api::V1::Accounts::Captain::CopilotMessagesController < Api::V1::Accounts::BaseController
+  before_action :current_account
+  before_action -> { check_authorization(Captain::Assistant) }
+  before_action :set_copilot_thread
+
+  def index
+    @copilot_messages = @copilot_thread
+                        .copilot_messages
+                        .order(created_at: :asc)
+                        .page(permitted_params[:page] || 1)
+                        .per(1000)
+  end
+
+  private
+
+  def set_copilot_thread
+    @copilot_thread = Current.account.copilot_threads.find_by!(
+      uuid: params[:copilot_thread_id], user_id: Current.user.id
+    )
+  end
+
+  def permitted_params
+    params.permit(:page)
+  end
+end

enterprise/app/controllers/api/v1/accounts/captain/copilot_threads_controller.rb

@@ -0,0 +1,19 @@
+class Api::V1::Accounts::Captain::CopilotThreadsController < Api::V1::Accounts::BaseController
+  before_action :current_account
+  before_action -> { check_authorization(Captain::Assistant) }
+
+  def index
+    @copilot_threads = Current.account.copilot_threads
+                              .where(user_id: Current.user.id)
+                              .includes(:user)
+                              .order(created_at: :desc)
+                              .page(permitted_params[:page] || 1)
+                              .per(5)
+  end
+
+  private
+
+  def permitted_params
+    params.permit(:page)
+  end
+end