Warn the organiser when the maximum number of participants of an event is changed
People on the waiting list don't get any notification and thus cannot know that their status changed.
The organiser should do a follow-up.
Steps to reproduce
- Create an event
- Enable x registrations
- Register at least x+1 people
- Change the number of registrations to x+1
- See that the person x+1 didn't get an email notification