iuk_builder: have systemd-tmpfiles maintain a dedicated, stable temporary directory
Once the isoworkers are upgrade to Trixie, chances are that /tmp is not large enough for this (it'll be backed by a tmpfs by default), so we are migrating the release process and the build_IUKs Jenkins job to use a new dedicated, stable temporary directory, that's deleted and re-created at boot time.
refs tails#20604 (closed)