Use internalPort to specify k8s' grpc probe ports

[elgbar]

Currently you have set all ports manually, even if they should be the same as common.service.internalPort so one have to write something like this:

common:
  grpc: true
  service:
    internalPort: &grpc_port 8091
  container:
    probes:
      liveness:
        grpc:
          port: *grpc_port
      readiness:
        grpc:
          port: *grpc_port
      startup:
        grpc:
          port: *grpc_port

It would be niceer to be shorten the config down to enabling the use of the new internal probes with a toggle, like so:

common:
  grpc: true
  service:
    internalPort: 8091
  container:
    probes:
      use_k8s_grpc: true # Explicitly enable internal probes here

[elgbar]

Whats the status on this issue?