containerd config patching should be version aware

[BenTheElder]

We should make containerd config patching work similarly to kubeadm config patching:

• 1. Check version key, if present, apply only patches with matching version or no version
• 2. Start using version in our patches / examples / registry script / ...
• 3. Start specifying both version 2 and version 3 patches in our examples where relevant
• 4. Warn users in release notes that a future release will switch to version 3 (I assume eventually containerd will require this? cc @chrishenzie)
• 5. Switch to version 3 after some number of releases of warning and supplying patches for both versions

For context, containerd config versions have all the same fields as far as I know, but the namespacing scheme has changed. Fields have been deprecated across config versions based on the containerd version, for e.g. #2875

[chrishenzie]

I assume eventually containerd will require this?

I think it should be required in that new features will only land in the latest config version

[BenTheElder]

I think it should be required in that new features will only land in the latest config version

ACK, that's much less of a problem than if it will be phased out. Thanks!

I still think we should migrate, but since we have split responsibility with users (e.g. https://kind.sigs.k8s.io/docs/user/local-registry/) we'll have to make it gradual and support version-aware patch targets.

Sounds like we can plan to do this long term but not urgently.