Starts building a zip of a published version, or of files and folders
of it, up to 10 GB; above that, use the Pennsieve agent. Poll
GET /public/archives/{id} until it's READY, then get a link. The
archive is kept for 72 hours.
Anonymous archives are never emailed: keep the id to come back to it.
Embargoed versions need signing in (401). Building costs the
selection's size from the day's anonymous allowance, and so does
every link.