Update models documentation

**Feature request**
It would be great to have notifications for handlers.

**Use case**
Many users need this functionality for production deployments.

**Implementation idea**
Add a new config option `enable_notifications` with default `false`.

Start by locating the models documentation, handler implementation, and configuration definitions. Read how existing options are documented and how handlers currently report events. Done means the notification option is documented with its default and the requested handler notification behavior is clearly specified and covered by the relevant project checks.

Written by the indexing model from the issue text.