Consider deprecating old core API

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

**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. First trace the configuration handling and existing data or event paths, then clarify which data should trigger notifications and how they should be delivered; completion would require the enable_notifications option to default to false and the requested behavior to be covered by tests.

Written by the indexing model from the issue text.