Implement LoggingAsync for GRPC Worker Services (#14604)

* Implement LoggingAsync for GRPC Worker.

* Add nullptr checks

* Fix BUILD file format

* Change LoggingAsync implementation

- Revert changes to *_rendezvous_mgr
- Implement logging primitives in session_mgr instead
- Implement ClearLogs
- Fixed C++ formating

* Check for nullptr

* Better handling of the case when both "clear" and "retrieve" flags are sent to "LogAsync."
nullptr check on default_worker_cache_.

* Fix formatting

* Updata session_mgr.cc to address changes in 619792fa