Implement 'bcachefs data scrub', frontend for
BCH_IOCTL_DATA.BCH_DATA_OP_scrub.
Takes a path to a device, mountpoint, or filesystem uuid. Can be run on
a specific device by passing a device, or if run on a filesystem scrubs
all devices in parallel.
Metadata only scrubbing is supported via -m.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>