Add stubs for new API:
* RecordWorkerHeartbeat
* ListWorkers
Also add feature flags
Adding new API is a breaking change, we need stubs.
Corresponding API PR:
https://github.com/temporalio/temporal/pull/7870
- [x] built
- [ ] run locally and tested manually
- [ ] covered by existing tests
- [ ] added new unit test(s)
- [ ] added new functional test(s)