Mutating Webhook Configurations side effect configuration

[phillebaba]

What steps did you take and what happened:

In a cluster where experimental mutation is enabled a mutatingwebhookconfigurations will be created in the cluster. If someone runs kubectl diff -f deployment.yaml against the cluster an error message will be returned.

Error from server (BadRequest): admission webhook "mutation.gatekeeper.sh" does not support dry run

This is occurs because sideEffects: Unknown is set on the webhook. According to the documentation if it is sett to Unknown or Some dry runs will automatically be rejected.
https://kubernetes.io/docs/reference/generated/kubernetes-api/v1.21/#mutatingwebhook-v1-admissionregistration-k8s-io

What did you expect to happen:

Expected diff to run without any issues.

Anything else you would like to add:

This seems like an important issue that should be fixed before the next release of gatekeeper. Is there a specific reason that sideEffects is not set or is it just missing by mistake.

Environment:

• Gatekeeper version: v3.4.0
• Kubernetes version: Server Version: version.Info{Major:"1", Minor:"19", GitVersion:"v1.19.7", GitCommit:"8ab00ff68a1763b5a506a7073cb8e67b12dfbcd7", GitTreeState:"clean", BuildDate:"2021-03-10T23:40:01Z", GoVersion:"go1.15.5", Compiler:"gc", Platform:"linux/amd64"}