MariadbMon documentation needs to take 10.5 privilege changes into account

Currently the MairadMon documentation says that the REPLICATION CLIENT privilege is needed as a minimum:

GRANT REPLICATION CLIENT on . to 'monitor_user'@'%';

Assuming that this privilege is mostly needed to execute SHOW SLAVE STATUS it needs to be replaced with

GRANT REPLICATION SLAVE ADMIN ON . to 'monitor_user'@'%'

for server versions 10.5 and later.

See also: https://mariadb.com/kb/en/changes-improvements-in-mariadb-105/#privileges-made-more-granular