change stash/restic backup target and offsite replication behaviour

[C0nsultant]

Right now, stash/restic is configured with BackBlaze as a direct storage backend. This is fine expect for the additional use of prune: true. This causes excessive download bandwith since restic downloads the entire repo for repacking after the prune. That bandwidth is (at least) 4x as expensive as the actual storage. More details in this thread.

Some ideas:

• Back up to a local target with prune and simply replicate (i.e. 1:1 sync) this to BackBlaze after
• Pruning is intended to remove data from the bucket that is not referenced by any snapshot. Considering that the backups here are append-only for the most part (databases, long-term storage of photos, documents, ...), running restic forget without --prune or a separate --prune schedule wit significantly reduced frequency should be fine. This would potentially result in the bucket size being larger as they then contain files that are not part of any active backup/snapshot. But again: The storage cost is only a small fraction of the data transfer cost.