Update maxscale.cnf default file

# Monitor for the servers

#

# This will keep MaxScale aware of the state of the servers.

# MariaDB Monitor documentation:

# https://mariadb.com/kb/en/maxscale-6-monitors/

#

# Create the monitor user with:

#

#  CREATE USER 'monitor_user'@'%' IDENTIFIED BY 'monitor_pw';

#  GRANT REPLICATION CLIENT, FILE, SUPER, RELOAD, PROCESS, SHOW DATABASES, EVENT ON *.* TO 'monitor_user'@'%';