Rename systemd debusine-server.debusine-server-artifacts-cleanup.* to debusine-server.debusine-server-cleanup.*

debusine-server.debusine-server-artifacts-cleanup.service invokes debusine-admin delete_expired which does more than only artifacts cleanup: rename it appropriately.

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information