ensure images with desired prefix and/or tag format don't get renamed/retaged on copy

[errordeveloper]

It should be possible to run this and avoid image being copied once again:

tape pull --image errordeveloper/foo:config.xyz --manifest-dir foo
tape package --ouput-image errordeveloper/foo --manifest-dir foo

This will come with a new digest, because of how source ephoch works, but there might be a way to avoid that too with #25 and #26.