Checks if image is in one of the allowed repositories.
See https://kubernetes.io/docs/admin/admission-controllers/#imagepolicywebhook
$ python main.py -h
$ python main.py myrepo
httpie POST http://localhost:8090/ @request-ok.json | jq
{
"apiVersion": "imagepolicy.k8s.io/v1alpha1",
"kind": "ImageReview",
"status": {
"reason": "",
"allowed": true
}
}