Get in the Cluster, Benji!

Here we introduce benji [1], a backup system based on backy2. It lets us
backup Ceph RBD objects from Rook into Wasabi, our offsite S3-compatible
storage provider.

Benji runs as a k8s CronJob, every hour at 42 minutes. It does the
following:
 - runs benji-pvc-backup, which iterates over all PVCs in k8s, and backs
   up their respective PVs to Wasabi
 - runs benji enforce, marking backups outside our backup policy [2] as
   to be deleted
 - runs benji cleanup, to remove unneeded backups
 - runs a custom script to backup benji's sqlite3 database into wasabi
   (unencrypted, but we're fine with that - as the metadata only contains
   image/pool names, thus Ceph PV and pool names)

[1] - https://benji-backup.me/index.html
[2] - latest3,hours48,days7,months12, which means the latest 3 backups,
      then one backup for the next 48 hours, then one backup for the next
      7 days, then one backup for the next 12 months, for a total of 65
      backups (deduplicated, of course)

We also drive-by update some docs (make them mmore separated into
user/admin docs).

Change-Id: Ibe0942fd38bc232399c0e1eaddade3f4c98bc6b4
6 files changed