[moby] Containerd image management integration

[cpuguy83]

Since contained 1.0, containerd now handles full container and image management lifecycle.

Much of this is duplicated in Moby (older codebase). The work item here is to migrate Moby to use containerd's image management.
Exercising containerd's full capabilities through Moby is a huge step towards ensuring stability of containerd which is at the core of basically all container workloads.

Work stream is happening here: moby/moby#38738
This is mainly being driven by Docker, but there are many TODO's in the change and needs help to get in.

I do not believe there is enough time to get this in for the next Docker release, however.

[cpuguy83]

Started teasing out some of the items in the PR that can be split out (like updating vendors, removing v1 schema support, etc) which helps simplify the PR a bit.

Also started looking at one of the TODO items which is to have moby keep pointers in the image metadata (stored in containerd) that points to the layer blobs which are already stored in the engine.
Basically the case here is a user upgrading and having layers in moby's layer store. Since we aren't going to migrate these blobs to containerd we just need some way for moby to know where to get them from for a given image.

[cpuguy83]

Picking this back up.
Currently working on migrating the plugins package to use containerd distribution: moby/moby#39946

[cpuguy83]

I'm not working on completing this, and it seems like someone from Mirantis is going to pick up this work, so closing this out.

Note the PR for migrating plugin to use containerd distribution code (#29 (comment)) is completed.