Borg handler compatibility with borg 1.2

Current borg handler is not fully compatible with borg 1.2.

• New warnings can cause a lot of noise (https://github.com/borgbackup/borg/issues/6379).
• We need to explicitly call borg compact (https://borgbackup.readthedocs.io/en/stable/usage/notes.html#separate-compaction)

I am working on a new version of the handler. I will submit my changes when they are well tested.