[POP-105] `probe` must use port number for GRPC

[jcpunk]

Describe the bug
For [POP-105] Liveness uses a port#, prefer a named port. GRPC services must use port numbers.

To Reproduce
Steps to reproduce the behavior:

1. setup a livenessProbe using GRPC and a port number
2. Run popeye
3. See [POP-105]

Expected behavior
Since GRPC probes must use numbers, this shouldn't report

Versions (please complete the following information):

• OS: Fedora
• Popeye 0.22.1
• K8s 1.34.1

Additional context
https://kubernetes.io/docs/reference/generated/kubernetes-api/v1.35/#grpcaction-v1-core