https://github.com/kubernetes/enhancements/blob/master/keps/sig-storage/177-volume-snapshot/tighten-validation-webhook-crd.md
1. Ratcheting validation webhook server image
2. Controller labels invalid objects
3. Unit tests for webhook
4. Deployment README and example deployment method with certs
5. Update top-level README
Racheting validation:
1. webhook is strict on create
2. webhook is strict on updates where the existing object passes strict validation
3. webhook is relaxed on updates where the existing object fails strict validation (allows finalizer removal, status update, deletion, etc)
Additionally the validating wehook server will perform immutability
checks on scenario 2 above.
Splitting out the RBAC definitions into a separate file has the
advantage that it can be used as-is without editing in other
deployments. For example, the kubernetes-csi/docs example can
use this rbac.yaml file instead of a local copy.
While at it, the upstream external-provisioner RBAC file gets used,
which fixes the too broad permissions for "endpoints".
