Initial version

This is the initial version for arch-release-promotion. The tooling is meant to promote our automated releases on gitlab (e.g. https://gitlab.archlinux.org/archlinux/releng/-/releases) using a valid packager PGP key to sign artifacts (releng#6 (closed)), while creating a few extra artifacts such as JSON consumable for archweb (releng#3 (closed)) and a torrent file (releng#5 (closed)). This additional promotion data is then attached to a respective release (which is then ready to be picked up by our server to consume it).