feat(server): add generate title cron resolver (#13189)

fix AI-350

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **New Features**
* Added a new option to manually trigger the generation of missing
session titles via a GraphQL query.

* **Improvements**
* The process for generating missing session titles now considers all
eligible sessions, without limiting the number processed at a time.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

packages/backend/server/src/__tests__/__snapshots__/copilot.spec.ts.md

@@ -431,9 +431,7 @@ Generated by [AVA](https://avajs.dev).
       ],
       modelCalls: [
         {
-          args: [
-            100,
-          ],
+          args: [],
         },
       ],
     }

packages/backend/server/src/__tests__/models/copilot-session.spec.ts

@@ -1078,7 +1078,7 @@ test('should get sessions for title generation correctly', async t => {
     })
   );
 
-  const result = await copilotSession.toBeGenerateTitle(10);
+  const result = await copilotSession.toBeGenerateTitle();
 
   t.snapshot(
     {