Log enabled controllers and warn if no controllers are enabled (#3710)

Because the default is to enable no controllers, it is easy to
mistakenly start a no-op controller.

Author: justinsb

porch/controllers/main.go

@@ -144,13 +144,21 @@ func run(ctx context.Context) error {
 	}
 
 	enabledReconcilers := parseReconcilers(enabledReconcilersString)
+	var enabled []string
 	for name, reconciler := range reconcilers {
 		if !reconcilerIsEnabled(enabledReconcilers, name) {
 			continue
 		}
 		if err = reconciler.SetupWithManager(mgr); err != nil {
 			return fmt.Errorf("error creating %s reconciler: %w", name, err)
 		}
+		enabled = append(enabled, name)
+	}
+
+	if len(enabled) == 0 {
+		klog.Warningf("no reconcilers are enabled; did you forget to pass the --reconcilers flag?")
+	} else {
+		klog.Infof("enabled reconcilers: %v", strings.Join(enabled, ","))
 	}
 
 	//+kubebuilder:scaffold:builder