Add TypeScript types for helpers

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

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

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

The issue names no files, tests, or entry points. First locate the helpers and the configuration handling for enable_notifications, then check how existing options are typed and tested. Done means the requested TypeScript helper types and the notification option with a false default are covered, after resolving the mismatch between the title and description.

Written by the indexing model from the issue text.