Support Ratify as a containerd plugin

[akashsinghal]

What would you like to be added?

Ratify's main scenario in k8s has been through admission controller integration with Gatekeeper. Although this is the prevailing solution today, there are many scenarios where this is less than ideal: large clusters where it becomes a single point of failure, multi-arch manifests, etc. Ratify should explore integrating into containerd as a plugin. Beyond image signature verification, Ratify's plugin support for all verification operations such as sbom, licensecheck, spdx, etc. can provide robust validation at the containerd level.

containerd tracking issue: https://github.com/containerd/containerd/issues/6691

Anything else you would like to add?

No response

Are you willing to submit PRs to contribute to this feature?

• [ ] Yes, I am willing to implement it.