Allow checking out an artifact as a 'tar' stream

I want to be able to checkout an artifact by streaming it to stdout as 'tar' data.

This would speed up two use cases:

• sometimes I want the artifact as an archive, and currently the only way to do that is to check it out to a directory, then run tar myself, then delete the directory
• sometimes I want to view the contents of an artifact, and currently the only way to do that is to check it out to a directory, run ls, then delete the directory