Finer grained auth system properties

Right now auth can be set to "from" and "to" (`-Djib.from.auth.username` for ex) but this is really not convenient in a multimodule project with multiple images, in particular when from images don't come from the same repo - docker.io, custom.foo for example.
Would be great to support something more specific like `-Djib.registries.docker.io.auth.username` or `-Djib.registries.1.2.3.4.auth.username` (ip) and password indeed.