Added support to BACKUP STAGE to maria-backup
This is a port of the code from ES 10.6
See MDEV-5336 for backup stages description.
The following old options are not supported by the new code:
--rsync ; This is because rsync will not work on tables
that are in used.
--no-backup-locks ; This is disabled as mariadb-backup will always
use backup locks for better performance.
due to different packaging issues.
Also, Percona thinks that tar support has many limitations
and should be removed as well( see discussion in
https://bugs.launchpad.net/percona-xtrabackup/+bug/1681721)
there is an alternative streaming format xbstream that is supported and
does not have these limitations.
