Add ability to filter objects on injection controller promotion

Currently we enqueue every object with no way to filter, which causes
problems for eventing's source controller which reconciles duck CRDs.

codegen/cmd/injection-gen/generators/reconciler_controller.go

@@ -217,6 +217,8 @@ func NewImpl(ctx {{.contextContext|raw}}, r Interface{{if .hasClass}}, classValu
 
 	lister := {{.type|lowercaseSingular}}Informer.Lister()
 
+	var promoteFilterFunc func(obj interface{}) bool
+
 	rec := &reconcilerImpl{
 		LeaderAwareFuncs: {{.reconcilerLeaderAwareFuncs|raw}}{
 			PromoteFunc: func(bkt {{.reconcilerBucket|raw}}, enq func({{.reconcilerBucket|raw}}, {{.typesNamespacedName|raw}})) error {
@@ -225,7 +227,11 @@ func NewImpl(ctx {{.contextContext|raw}}, r Interface{{if .hasClass}}, classValu
 					return err
 				}
 				for _, elt := range all {
-					// TODO: Consider letting users specify a filter in options.
+					if promoteFilterFunc != nil {
+						if ok := promoteFilterFunc(elt); !ok {
+							continue
+						}
+					}
 					enq(bkt, {{.typesNamespacedName|raw}}{
 						Namespace: elt.GetNamespace(),
 						Name: elt.GetName(),
@@ -274,6 +280,9 @@ func NewImpl(ctx {{.contextContext|raw}}, r Interface{{if .hasClass}}, classValu
 		if opts.DemoteFunc != nil {
 			rec.DemoteFunc = opts.DemoteFunc
 		}
+		if opts.PromoteFilterFunc != nil {
+			promoteFilterFunc = opts.PromoteFilterFunc
+		}
 	}
 
 	rec.Recorder = createRecorder(ctx, agentName)