Extension to check if all images of a tree are present on a registry

[mudler]

This is needed for pre-release QA.

We need an extension that checks that all package cache images are present in a remote registry from a given point in history of a tree (practically, a git tag).

Action items:

• Write the extension which uses luet-tree images to retrieve images hashes, and enhancing it to output builder images too
• Adapt the mos/desktop pipeline here https://github.com/mocaccinoOS/desktop/blob/d401643d063ad43fdd2fda7339feebcb14d87e4e/.github/workflows/build_k8s.yml#L46 to do the check prior to move artifacts to stable buckets