OpenPlex 0.28.0

feat(backups): warn when backups are not off the server

The Backups page now says where the repository is compared with the data
it protects. A local repository is traced through /proc/self/mountinfo
and /sys/class/block down to physical disks (partitions, LVM, RAID,
dm-crypt, btrfs; ZFS by pool): on the data's disk it warns, on another
disk it notes that losing the server would still take both, and on a
network filesystem it is off-site. An S3 endpoint that resolves to this
server's own addresses is warned about too.