Use case:
- azure nodes needs the extra python3-swh.objstorage.cloud package (workers,
vault)
- ceph machines needs (needed?) python3-swh.objstorage.rados
Using this new option, `azure_euwest` location defines the extra `python3-swh.objstorage.cloud`
dependency.
Thus rendering obsolete some extra `objstorage_cloud` class (which was a `temporary` hack IIRC).