Consider deprecating old controllers API

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

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

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

The title and body describe different work: deprecating an old controllers API versus adding configuration notifications. Start by locating the configuration handling and notification entry points, then clarify which goal is intended. Done should include an agreed scope, the enable_notifications default, and production deployment behavior.

Written by the indexing model from the issue text.