Expose the anchoring system

[realshuting]

          > Hi @ltearno - thanks for sharing your use case with us. This change looks fine, and I would like to understand more about how you use Kyverno as a lib, specifically, what components you are using? We are planning to expose re-usable components via https://github.com/kyverno/pkg and your use case would definitely help us structure the lib.

Hi, thanks for the merge!
We are using the anchoring system you developped above kustomize's patchstrategicmerge.
We found your technic a great way to filter changes that we want to apply to manifests.
Thanks again!

Originally posted by @ltearno in kyverno/kyverno#9887 (comment)