git-lfs is ignored

[waldheinz]

The fact that a git repo uses git-lfs is completely ignored by Hydra. This means that an invocation of

nix build 'git+ssh:https://git@my-gitlab-instance/foo/foo.git'

on a system where git-lfs is in $PATH can actually produce a different result than configuring the exact same flake URI in Hydra (or any system where git-lfs is not in $PATH I assume, though I did not test this).

I think we agree that this is a problem, but I'm not sure what should be the direction here. It would be nice if repos using lfs just worked, but if that's not possible maybe the clone should fail, telling the user that lfs is not supported?