Support grpc readiness probing use case

### Is your feature request related to a problem?
We have a scenario where we are starting a VM and would like to detect that a gRPC service on the VM is up. We want to have the communication to be directed from the starting host to the VM rather than the other way round because many VMs are being started at the same time and we want to avoid overloading the host initiating the creations while parallelizing the VM creation as much as possible. Therefore we would like to have a way using gRPC to check if the gRPC connection is possible while minimizing both the resources spent on the initiating side for polling and the time between the service being up and the connection being established.

### Describe the solution you'd like
We were expecting to rely on the underlying gRPC TCP reconnection framework. Using the channel.getState and channel.notifyWhenStateChanged we are able to implement the polling. However the 2 minute maximum backoff is slightly larger than we would like - effectively we would like a fairly steady rate of polling.

### Describe alternatives you've considered
We can mostly reimplement our own backoff policy by calling resetConnectBackoff() at appropriate times but that feels like abusing the API. We can also implement the readiness checking outside of gRPC but it seems that most of the infrastructure is already there so it would be nice to be able to reuse it.

### Additional context
I'm aware of https://github.com/grpc/grpc-java/issues/9353 and https://github.com/grpc/grpc-java/issues/10932. That being said the latter issue had a slightly different use case and in the first issue it seemed that the main blocker was a lack of clear motivating problem - here I'm presenting one so I'd like to get feedback whether this idea would make sense for this use case.

Inizia con le API channel.getState e channel.notifyWhenStateChanged, quindi esamina resetConnectBackoff e le issue correlate grpc-java#9353 e grpc-java#10932. Definisci in che modo il rilevamento della disponibilità dovrebbe controllare il polling e il backoff della riconnessione senza richiedere ai chiamanti di reimplementarli. Il lavoro è completato quando il comportamento proposto è specificato e coperto da test appropriati del progetto.

Scritto dal modello di indicizzazione a partire dal testo della issue.