fix: Update specs, add background response job implementation for copilot threads (#11600)

- Enable jobs by default when a copilot thread or a message is created.
- Rename thread_id to copilot_thread_id to keep it consistent with the
model name
- Add a spec for search_linear_issues service

enterprise/app/services/captain/tools/copilot/search_linear_issues_service.rb

@@ -46,7 +46,7 @@ class Captain::Tools::Copilot::SearchLinearIssuesService < Captain::Tools::BaseS
   end
 
   def active?
-    @user.present? && @assistant.account.hooks.find_by(app_id: 'linear').present?
+    @user.present? && @assistant.account.hooks.exists?(app_id: 'linear')
   end
 
   private