https://book.kubebuilder.io/cronjob-tutorial/webhook-implementation.html
> If you want to implement admission webhooks for your CRD, the only thing you need to do is to implement the Defaulter and (or) the Validator interface.

だよね，your CRDが対象であって，それ以外のリソースにwebhook仕掛けるのはコレじゃないよね