GC: allow ignored resources to be customized

Allow the list of resources the garbage collector controller should
ignore to be customizable, so downstream integrators can add their own
resources to the list, if necessary.

cmd/kube-controller-manager/app/core.go

@@ -189,7 +189,20 @@ func startGarbageCollectorController(ctx ControllerContext) (bool, error) {
 	metaOnlyClientPool := dynamic.NewClientPool(config, restMapper, dynamic.LegacyAPIPathResolverFunc)
 	config.ContentConfig = dynamic.ContentConfig()
 	clientPool := dynamic.NewClientPool(config, restMapper, dynamic.LegacyAPIPathResolverFunc)
-	garbageCollector, err := garbagecollector.NewGarbageCollector(metaOnlyClientPool, clientPool, restMapper, deletableGroupVersionResources, ctx.InformerFactory)
+
+	ignoredResources := make(map[schema.GroupResource]struct{})
+	for _, r := range ctx.Options.GCIgnoredResources {
+		ignoredResources[schema.GroupResource{Group: r.Group, Resource: r.Resource}] = struct{}{}
+	}
+
+	garbageCollector, err := garbagecollector.NewGarbageCollector(
+		metaOnlyClientPool,
+		clientPool,
+		restMapper,
+		deletableGroupVersionResources,
+		ignoredResources,
+		ctx.InformerFactory,
+	)
 	if err != nil {
 		return true, fmt.Errorf("Failed to start the generic garbage collector: %v", err)
 	}