These dockerfiles will be consumed by the github action, that will
build docker images and upload to our ghcr.io registry. The new image
will be used later by the open-iscsi test.

There isn't a clear way to tell when the image should be rebuilt
automatically. In theory it should be when the relevant debian package
gets an update or when a new Debian version is released. In practice,
these are annoying to track, so the action is to be invoked on demand.