Update validation documentation

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

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

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

No files, tests, or entry points are named. Start by locating the route handling and configuration code, then determine how notifications should be triggered and where the new option is documented. Done means the option defaults to false and route notifications work as described, with validation coverage.

Written by the indexing model from the issue text.