Allow building arbitrary images derived from a container image

[Conan-Kudo]

In the last community meeting, we discussed allowing the usage of container images as a "seed" for building any type of image, rather than just restricting it to container images as we do now.

Obviously, some part of this functionality exists in the stackbuild plugin, but it makes sense to start considering bringing more of that functionality into the core as multiple stakeholders have expressed interest in this functionality being part of the core.

This issue is filed to track this item.

[Conan-Kudo]

cc: @davide125 @travier

[uecasm]

FYI, I had a requirement to do this (and the stackbuild plugin didn't quite do it for me) but I was able to achieve it by extracting a tarball image and then using kiwi-ng system prepare --allow-existing-root.

The hard part was getting docker to generate a coherent tarball from an image in the first place. There are likely better tools for that job.

[github-actions]

This issue is stale because it has been open 60 days with no activity. stale label was set.