samba-tool: Filter confidential attributes out of backups made with the ‘--no-secrets...

samba-tool: Filter confidential attributes out of backups made with the ‘--no-secrets’ option

Without this change, ‘lab domains’ and backups intended not to contain
secrets will still contain confidential information, such as BitLocker
recovery data and KDS root keys. Add a new class that filters these
attributes out.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=15852

Signed-off-by: Jennifer Sutton <jennifersutton@catalyst.net.nz>
Reviewed-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>