Configuration setting names use the old mariabackup name when the executable name is now mariadb-backup

The name of the mariabackup executable has been renamed to mariadb-backup to keep it consistent with the other tool names. The configuration settings in MaxScale still use the old name mariabackup. To support the new name, we should provide aliases for either a generic name (e.g. backup like is used for backup_storage_address) or rename to the new name of the executable (i.e. mariadb_backup_parallel).

Original title: MaxScale fails to start when using mariadb-backup_parallel in configuration file
Original description:
In our documentation it says we can use the following mariadb-backup_parallel=2 to set the number of parallel for mariadb-backup when rebuilding a replica/backing up using MaxScale. However when I use this in a configuration file MaxScale fails to start with the following error:

error  : (Replication-Monitor); mariadbmon: The parameter 'mariadb-backup_parallel' is unrecognized.

Is this something that can actually be used? I blindly tried variations with no success mariadb-backup-parallel and mariadb_backup_parallel