handle the uffizi content store being full

The uffizi content storage is getting dangerously close to full.

After discussing our requirements (redundancy, migration to ceph, archiver issues), the following plan is being put into place:

1. reduce archiver lag and improve redundancy : Synchronously write all objects to azure as well as local storage
2. reduce local storage requirements : Stripe the local storage of contents across uffizi and banco
3. prepare the ceph migration, improve redundancy : Synchronously write a copy of the objects in ceph, with the final redundancy requirements (erasure coding, 5 chunks + 2 parity chunks), but with a more risky failure domain (OSD instead of host).
4. reclaim storage space : remove already backed up objects from uffizi and banco
5. future-proof the system : adapt the archiver to handle striped storages

---

Migrated from T1043 (view on Phabricator)