Support gRPC probes for Kubernetes, Openshift and Knative

[Sgitario]

Description

Apart from the existing probes protocols HTTP, TCP and unix commands, in Kubernetes v1.23 the gRPC protocol can also be used. More context in kubernetes.io/define-a-grpc-liveness-probe.

If your application implements gRPC Health Checking Protocol, kubelet can be configured to use it for application liveness checks. You must enable the GRPCContainerProbe feature gate in order to configure checks that rely on gRPC.

Here is an example manifest:

apiVersion: v1
kind: Pod
metadata:
  name: etcd-with-grpc
spec:
  containers:
  - name: etcd
    image: k8s.gcr.io/etcd:3.5.1-0
    command: [ "/usr/local/bin/etcd", "--data-dir",  "/var/lib/etcd", "--listen-client-urls", "http://0.0.0.0:2379", "--advertise-client-urls", "http://127.0.0.1:2379", "--log-level", "debug"]
    ports:
    - containerPort: 2379
    livenessProbe:
      grpc:
        port: 2379
      initialDelaySeconds: 10

User story

Given an user who configures the new `dekorate.kubernetes.liveness-probe.grpcPort` property
When dekorate generates the kubernetes or openshift or Knative or other relevant manifests
Then the liveness probes should be generated using the new `grpc` section

Given an user who does NOT configure the new `dekorate.kubernetes.liveness-probe.grpcPort` property
When dekorate generates the kubernetes or openshift or other relevant manifests
Then the liveness probes should NOT be generated using the new `grpc` section

The new field grpcPort should be added in the Probe java class which is also used for readiness, startup (when implemented in #854) probes.

Acceptance criteria

• Add integration tests for K8s, Knative and Openshift
• Update documentation with new configuration

[Sgitario]

Update: it seems that the gRPC probe will be available also in readiness, startup and liveness, not only in liveness: https://www.infoq.com/news/2021/12/kubernetes-1-23/

Description updated accordingly.