admission controller types

[clux]

AdmissionReview / AdmissionRequest / AdmissionResponse do not have generated types in k8s-openapi.

This is possibly (speculation) for good reasons; the way they work is very different from a normal api call: https://kubernetes.io/blog/2019/03/21/a-guide-to-kubernetes-admission-controllers/

The types however are present in kuberenetes/api/admission, and don't see how people can do admission controllers without them.

I imagine we could provide a module that hand-rolled those structs, make them generic over the Resource trait, and it might not be that bad?

Have not had much time to look at this, but it could be a nice clean feature for someone to try, and am happy to review PRs. Marking as help wanted, but it's probably not easy.

Testing wise, a web server would pull in a lot of deps, but maybe we could do something light with warp or hyper as an example.

[clux]

This is now officially released in 0.53. Though it did receive a number of minor tweaks in master from #488, #498, #499, #507, #509.

Thanks again!