Feature Request: allow operators to provide custom rejection message

[flavio]

Is your feature request related to a problem?

As an operator, I would like to give more context to my users when an operation is rejected by a Kubewarden policy.
For example, I would like to point the users to an internal WIKI where the error message is explained and the remediation paths are illustrated.

Currently, the rejection message originated by a policy is the one hard coded by the policy author.

Solution you'd like

When deploying a policy, have a way to define an additional error message to be reported back to the user. Maybe this could be set on the ClusterAdmissionPolicy/Admission Policy CRD

Alternatives you've considered

No response

Anything else?

Technically speaking, we could add the user defined messages as Warnings inside of the AdmissionResponse object.

See here