Ensure that informers have the namespace index

Most of the lister logic (both here and in Kubernetes generate listers)
assume that the namespace index is present by default, so we should
always set it up.

Author: DirectXMan12

pkg/cache/internal/informers_map.go

@@ -158,7 +158,9 @@ func (ip *InformersMap) Get(gvk schema.GroupVersionKind, obj runtime.Object) (*M
 		if err != nil {
 			return nil, err
 		}
-		ni := cache.NewSharedIndexInformer(lw, obj, ip.resync, cache.Indexers{})
+		ni := cache.NewSharedIndexInformer(lw, obj, ip.resync, cache.Indexers{
+			cache.NamespaceIndex: cache.MetaNamespaceIndexFunc,
+		})
 		i = &MapEntry{
 			Informer: ni,
 			Reader:   CacheReader{indexer: ni.GetIndexer(), groupVersionKind: gvk}}