Add new user for general monitoring

[derekperkins]

I think it would be generally useful to add a default monitoring user with minimal permissions that cover a standard range of MySQL collection agents. Here is a set pulled from the datadog docs:

mysql> GRANT REPLICATION CLIENT ON *.* TO 'monitoring'@'localhost' WITH MAX_USER_CONNECTIONS 5;

mysql> GRANT PROCESS ON *.* TO 'monitoring'@'localhost';

For MySQL 8.0+ set max_user_connections with:
mysql> ALTER USER 'monitoring'@'localhost' WITH MAX_USER_CONNECTIONS 5;

mysql> GRANT SELECT ON performance_schema.* TO 'monitoring'@'localhost';