Support "ADD --unpack" instruction

[cnd4]

Feature request description

Docker supports the --unpack argument for the ADD instruction: https://docs.docker.com/reference/dockerfile/#add---unpack

Unfortunately, when I try to run a Containerfile with ADD --unpack=true, I get the following error:

[3/6] STEP 3/3: ADD --unpack=true "https://example.com/archive.tar.gz" /                                     
Error: building at STEP "ADD --unpack=true "https://example.com/archive.tar.gz" /": ADD only supports the --chmod=<permissions>, --chown=<uid:gid>, --checksum=<checksum>, --link, --keep-git-dir, and --exclude=<pattern> flags

It would be nice to support this unpacking argument.

Suggest potential solution

If possible, I would want Podman to understand and execute ADD --unpack=true instruction.

Have you considered any alternatives?

The current alternative is to ADD the archive and add a RUN instruction in order to unpack the archive. It creates another layer so this solution may not be the best.

Additional context

No response

[baude]

I'm going to move this to buildah because they provide all the building capability for podman. thanks for your issue write up.