Allow "alert" script to be executed when errors or warnings are logged

It would be a very useful feature if MaxScale could allow an "alert" script to be executed anytime errors or warnings are logged.

The more granular this would be, the better (perhaps it could be a comma-delimited list of error/warning code values).

To give an example, someone wants to be able to be notified immediately, via a script from MaxScale, when they see the following error ("Too many connections"):

2020-04-01 10:00:01 error : Unable to write to backend 'server1' due to authentication failure. Server in state RUNNING SLAVE.

2020-04-01 10:00:01 error : (661327) Invalid authentication message from backend 'server1'. Error code: 1040, Msg : #08004Too many connections