See coop-cloud/organising#258
This fixes also how we read the digest of the image. I think it was
wrong before. Some registries restrict reading this info and we now just
default to "unknown" for that case.
This also appears to bring a wave of new dependencies due to the generic
handling logic of containers/... package. The abra binary is now 1mb
larger.
The catalogue generation is now slower unfortunately. But it is more
robust.
The generic logic looks in ~/.docker/config.json for log in details, so
you don't have to pass those in manually on the CLI anymore. We just
read those defaults. You can "docker login" to get credentials setup in
that file. Since most folks won't generate the catalogue, this seems
fine for now.
