Custom priority for exceptions and events

[Tomas2D]

Hello, I really appreciate the work that you have made on this library, it is exactly what I was looking for.

The main reason for me to use this package is to message me, once the server is not able to start up after some restarts. The problem is that my e-mail inbox receives tons of e-mails with the same information value -> The application cannot boot up.

The possible solution would be to allow set custom priority for exceptions or at least for events. At this time, the events has high priority and thus bypasses the batchMaxMessages and batchPeriodM as mentioned in https://github.com/pankleks/pm2-health#message-batching.

Are you will to add this feature or at least can I do a PR for this?

Thanks.