Add HTTP 429 Too Many Requests as a possible generic error response

Author: js-nh

CHANGELOG.md

@@ -8,6 +8,12 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 Note that in line with [Django REST framework policy](https://www.django-rest-framework.org/topics/release-notes/),
 any parts of the framework not mentioned in the documentation should generally be considered private API, and may be subject to change.
 
+## [Unreleased]
+
+* Added `429 Too Many Requests` as a possible error response in the OpenAPI schema.
+
+### Added 
+
 ## [7.0.0] - 2024-05-02
 
 ### Added