Use "numeric-ids" instead of "numeric-owner" in borg storage backend

Borg 1.2 deprecates the option "numeric-owner" in favour of "numeric-ids". We use the option in BorgStorageCommands.create_archive() and BorgStorageCommands.extract_archive(). Since Borg 1.2 (or later) will be in the upcoming stable debian (bookworm) we will need to change those.