feat: Skip preflight on Cluster update

This is defensive programming. The webhook is already configured to only
run on create. When we support for update, we will remove this, and
reconfigure the webhook.

Author: dlipovetsky

pkg/webhook/preflight/preflight.go

@@ -84,6 +84,10 @@ func (h *WebhookHandler) Handle(ctx context.Context, req admission.Request) admi
 		return admission.Allowed("")
 	}
 
+	if req.Operation == admissionv1.Update {
+		return admission.Allowed("")
+	}
+
 	cluster := &clusterv1.Cluster{}
 	err := h.decoder.Decode(req, cluster)
 	if err != nil {