Merge pull request #50012 from deads2k/cli-17-discovery

Automatic merge from submit-queue

use specified discovery information if possible

Fixes kubernetes/kubernetes#49948

This uses the available discovery information if available, but it seems we never updated "normal" resources to show the singular name, so its often not available.  I've left this code compatible.

@enisoc @ash2k 
@kubernetes/sig-api-machinery-misc 

```release-note
custom resources that use unconventional pluralization now work properly with kubectl and garbage collection
```

Kubernetes-commit: e190f391129260527c119fe319216212c916ae5d

pkg/api/meta/restmapper.go

@@ -117,7 +117,10 @@ func NewDefaultRESTMapper(defaultGroupVersions []schema.GroupVersion, f VersionI
 
 func (m *DefaultRESTMapper) Add(kind schema.GroupVersionKind, scope RESTScope) {
 	plural, singular := UnsafeGuessKindToResource(kind)
+	m.AddSpecific(kind, plural, singular, scope)
+}
 
+func (m *DefaultRESTMapper) AddSpecific(kind schema.GroupVersionKind, plural, singular schema.GroupVersionResource, scope RESTScope) {
 	m.singularToPlural[singular] = plural
 	m.pluralToSingular[plural] = singular