[cert-manager]: Migrate Mutating- and ValidatingWebhookConfiguration

[databus23]

For the upcoming k8s upgrade to 1.22 we need to migrate WebhookConfiguration and ValidatingWebhookConfiguration to v1.

See https://kubernetes.io/docs/reference/using-api/deprecation-guide/#webhook-resources-v122

I actually can't find a reference to the respective yaml in this repo. There is a reference to a cert-manager chart in our chartmuseum in the kube-system-* charts.
We need to ensure sure that the chart does not contain deprecated and removed api versions for webhook resources.