Add rate limiting for notifications

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

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

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

First reconcile the title about notification rate limiting with the body, which requests retry for config and an `enable_retry` option. Locate the configuration handling and retry-related entry points, then confirm the intended behavior and tests; done should include a documented default of `false` and clear coverage for the requested retry behavior.

Written by the indexing model from the issue text.