Exceptions of lease keepAlive can be perceived

[tunefun]

Is your feature request related to a problem? Please describe.
Here is the keepAlive method: public synchronized CloseableClient keepAlive(long leaseId, StreamObserver<LeaseKeepAliveResponse> observer)

When some exceptions happened, such as connection failed, keekAlive will automatically restart, but there are no logs or callbacks, if deadline comes before fault recovery, onCompleted method of StreamObserver will be called, but we don't know what happened.

Describe the solution you'd like
I'd like onError method of StreamObserver should be called when some exceptions happened in lease keepAlive