Integration with k8s Validating Admission Policy for audit

[ritazh]

Describe the solution you'd like
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https://kubernetes.io/docs/reference/access-authn-authz/validating-admission-policy/

Anything else you would like to add:
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This is now possible with the multi-agent support in framework.

Environment:

• Gatekeeper version:
• Kubernetes version: (use kubectl version):

[ritazh]

There are two components to this:

1. audit: it is currently blocked on container-runtime v0.15.0 release in order to add K8sNativeValidation (cel) as a driver
   2. admission (GK controller to create ValidatingAdmissionPoicy resources from CT and constraints): this can start now

[sozercan]

ref open-policy-agent/frameworks#331

[ritazh]

1 is addressed by #2819