Client side error reporting in GRPC generated classes

### Describe the feature

Currently an exception that happens on the server (being passed to completable.fail) cannot be easy captured and thrown on the client side using the generated client classes. An existing PR has attempted to address this gap: https://github.com/eclipse-vertx/vertx-grpc/pull/194 but seems to have been stuck since august. There may be a simpler way to address this.

From a client API perspective, the error that is passed to handler from Promise.onFailure should capture the message/throwable that was passed to Completable.fail. IF serialization is an issue then the message alone would suffice. Currently only the status code is passed back to the client which makes debugging/client side reporting very opaque.

### Contribution

_No response_