Add TieringService heartbeat RPC interface for communication with Tiering Services

### Search before asking

- [x] I searched in the [issues](https://github.com/alibaba/fluss/issues) and found nothing similar.


### Description

Add TieringService heartbeat gRPC interface for communication with Tiering Services

### Willingness to contribute

- [ ] I'm willing to submit a PR!