Consider deprecating old controllers API

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

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

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

The issue does not name files, tests, or an entry point. Start by locating middleware handling and the configuration parser, then determine where notification behavior belongs. Done should include a documented enable_notifications option defaulting to false and a clear way to verify middleware notifications during production deployments.

Written by the indexing model from the issue text.