use `borg compact` after removing borg archives

Summary

Backup made with borg never free up the space after deleting versions.

Steps to reproduce

1. enable backup on a web area, with borg
2. make the backup
3. delete the backup

Correct behaviour

used space for the backup is 0, or at most unchanged from before, instead the space remained used

Environment

Server OS + version: Debian 12 ISPConfig version: 3.2.12p1 Software version of the related software: borg 1.4.0

Proposed fix

One needs to run borg compact to reclaim the space, after having done borg delete to delete an archive.