Create and save the Galera source archive

We need at least one source of truth for storing and archiving the galera sources.
One is GitHub Releases but it doesn't resolve submodules, see: https://github.com/orgs/community/discussions/31795

The other was mirror.mariadb.org | archive.mariadb.org
but Foundation Buildbot doesn't produce the sources on its CI staging storage i.e. ci.mariadb.org

This caused packaging issues downstream,
see: https://mariadb.zulipchat.com/#narrow/channel/118759-general/topic/Galera.20release.20notes/near/619514560

Suggested change:
Migrate buildbot configuration around galera sources from old buildbot:
https://buildbot.mariadb.net/buildbot/builders/kvm-src-rocky9-amd64-gal/builds/107

to buildbot.mariadb.org
and upload the archive on ci.mariadb.org to be picked up by Foundation's release workflow (faust)