fix: close #101 and fallback to internalPort for grpc probes

[AlexanderBrevig]

Specifying true will use internalPort.

          probes:
            grpc: true

[AlexanderBrevig]

The previous was a bit verbose:

          probes:
            liveness:
              grpc:
                port: 8080
            readiness:
              grpc:
                port: 8080
            startup:
              grpc:
                port: 8080

[AlexanderBrevig]

I'm also concidering this

          probes:
            grpc: true