Let disable webhooks

[This change](https://github.com/kubernetes-sigs/cluster-api/commit/280db9a796d5e1c2b3b75aa3036fcfe44f669909#diff-a46ea7e53a9e71ee7642[…]57385a613ca5d51cL170-L173) made webhooks to always run as part of the manager.

I'd like to keep the ability to disable running webhooks. Motivation is as adopting and building atop CAPI I’d like to do so gradually, going all in once with webhooks increase complexisty and resistance.

Also this is necessary to support other type than single controller deployments and should be part of this contract https://master.cluster-api.sigs.k8s.io/developer/architecture/controllers/support-multiple-instances.html#contract

Author: enxebre

main.go

@@ -143,7 +143,7 @@ func InitFlags(fs *pflag.FlagSet) {
 		"The minimum interval at which watched resources are reconciled (e.g. 15m)")
 
 	fs.IntVar(&webhookPort, "webhook-port", 9443,
-		"Webhook Server port")
+		"Webhook Server port. Set 0 to disable it.")
 
 	fs.StringVar(&webhookCertDir, "webhook-cert-dir", "/tmp/k8s-webhook-server/serving-certs/",
 		"Webhook cert dir, only used when webhook-port is specified.")
@@ -311,6 +311,10 @@ func setupReconcilers(ctx context.Context, mgr ctrl.Manager) {
 }
 
 func setupWebhooks(mgr ctrl.Manager) {
+	if webhookPort == 0 {
+		return
+	}
+
 	if err := (&clusterv1.Cluster{}).SetupWebhookWithManager(mgr); err != nil {
 		setupLog.Error(err, "unable to create webhook", "webhook", "Cluster")
 		os.Exit(1)