Support project archive upload

[dchaley]

Follow-up to #15

Support remote URIs that end in .gz. Archive the temporary directory then upload the archive to remote storage.

It's unclear if we actually need this. It's not super hard for users to cp -r. Still, that only works if the remote storage is actually in 1 shared root. Whereas we could combine files across roots into a VeryConvenient™️ archive.