Webhook and validation migration required

[theunrepentantgeek]

The release notes for the latest version of Kubebuilder include this:

This release introduces significant changes, especially for projects using webhooks.
Notably, the webhook.Validator and webhook.Defaulter interfaces are deprecated and will be removed in the next controller-runtime release (v0.20.0).
Please migrate to the new CustomValidator and CustomDefaulter interfaces.
Additionally, webhooks should now be placed in the internal/webhook directory. (You might want to see the webhooks implementation for the Cronjob Tutorial Sample)

We should look into doing this in our own time, so we're not facing time pressures by a critical update.