CI - Implement tests for ValidatingAdmissionPolicies

Following the rewriting of kyverno validating policies as ValidatingAdmissionPolicies in !3779 (merged) , it would be useful to have a test in CI to check they are effective.

Ideally, we should try to use kyverno chainsaw, as this tool has been built for that purpose.

In order to be easily reusable outside of gitlab, these tests should ideally be implemented as a test unit that would execute tests within a container.

The chainsaw test files could be defined in a kustomization that would embeed them in configmaps, consumed by some jobs executing chainsaw test.