Detection of images with multiple names through their Digest

One can check if two image names target the same image by checking their "Digest".

• in walt local repo, by using podman inspect <fullname> and checking the "Digest" field
• in docker local repo, by using skopeo inspect docker-daemon:<fullname> and checking the "Digest" field
• on the docker hub, by using skopeo inspect docker://<fullname> and checking the "Digest" field

This could be used to:

• improve performance of walt image clone (for instance, even if the user specified a hub image, we may target a local name in walt repo instead; interaction with the docker hub may also often be more efficient than with local docker daemon...)
• improve user friendliness of walt image search by letting the user know that a remote image is the same as one of his images (maybe indicate "same as: " in the cloneable link column)

The issue names walt image clone and walt image search as the entry points; start by examining how they identify local, Docker daemon, and Docker Hub images. Compare the Digest values from podman inspect and skopeo inspect. Done means the desired clone performance and same-image indication in search are defined and implemented.