This is required to enable External Authorization for gRPC, and to complete the external authorization story.

Related (Gateway API): https://issues.redhat.com/browse/OSSM-983

As a workaround, this field is accessible via the "techPreview" configuration today.

Acceptance criteria:

Users can deploy SMCP v2.4 with envoyExtAuthzGrpc:

apiVersion: maistra.io/v2
kind: ServiceMeshControlPlane
metadata: 
  name: basic
spec: 
  meshConfig: 
    extensionProviders: 
    - name: ext-authz
      envoyExtAuthzGrpc: 
        service: ext-authz.foo.svc.cluster.local
        port: 8000
        ...

The implementation will be almost 1:1 copy of this pull request: https://github.com/maistra/istio-operator/pull/1136.