What is the problem you're trying to solve

The vnd.docker.image.rootfs.diff.tar.zstd has existed in the real world because we can build it with buildkit . Buidkit avoids these with workarounds.
moby/buildkit#3968

Why don't we just treat it the same way as oci media type, so we can deal with it?

Describe the solution you'd like

1. Define vnd.docker.image.rootfs.diff.tar.zstd in https://github.com/distribution/distribution/blob/v2.7.1/docs/spec/manifest-v2-2.md#media-types
2. Support vnd.docker.image.rootfs.diff.tar.zstd in containerd

Additional context

No response