Merge pull request #59809 from phsiao/59733_port_forward_with_target_port

Automatic merge from submit-queue (batch tested with PRs 59809, 59955). If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.

kubectl port-forward should resolve service port to target port

**What this PR does / why we need it**:

Continues on the work in #59705, this PR adds additional support for looking up targetPort for a service, as well as enable using svc/name to select a pod.

**Which issue(s) this PR fixes**:
Fixes #15180
Fixes #59733

**Special notes for your reviewer**:

I decided to create pkg/kubectl/util/service_port.go to contain two functions that might be re-usable.

**Release note**:
```release-note
`kubectl port-forward` now supports specifying a service to port forward to: `kubectl port-forward svc/myservice 8443:443`
```

pkg/kubectl/cmd/util/factory_object_mapping.go

@@ -403,6 +403,13 @@ func (f *ring1Factory) AttachablePodForObject(object runtime.Object, timeout tim
 			return nil, fmt.Errorf("invalid label selector: %v", err)
 		}
 
+	case *api.Service:
+		namespace = t.Namespace
+		if t.Spec.Selector == nil || len(t.Spec.Selector) == 0 {
+			return nil, fmt.Errorf("invalid service '%s': Service is defined without a selector", t.Name)
+		}
+		selector = labels.SelectorFromSet(t.Spec.Selector)
+
 	case *api.Pod:
 		return t, nil