Pull only layers not yet present in local container storage

[ricardomaraschini]

When pulling images from tagger a whole tar file is sent down the line with the whole image, this is bad. Implement some caching validation so we can avoid pulling multiple times the same blobs.

We have two distinct possibilities here:

1. Reimplement tagio to mimic a registry api server.
2. Simply keep using GRPC but split the type used (instead of tar use dir transport and transfer blob by blob).

[ricardomaraschini]

Still needs some extra discussions on this one.

[otaviof]

I think we are looking for a local container storage, analogous on what we have with Docker/Podman. So, kubectl tag pull will interact with this underlying storage, and by taking advantage of the registry protocol, will download only the layers it needs.

Upstream we see containers/storage we the primary implementation for this logic.

[otaviof]

Another perspective to consider, is how users will consume this feature. If I understand it correctly, I could:

1. Download the container image with kubectl tag pull <image>;
2. Use this container with docker, podman, buildah. For instance docker run --rm <image>;

Therefore, we need to consider how tagger plugin interacts with Docker API and local OCI container storage. As a starting point, we should focus on OCI storage, but keep this design in mind.