chore: update changelog for added secondary sort by id

Author: Yuri Zmytrakov

CHANGELOG.md

@@ -8,6 +8,8 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 ## [Unreleased]
 
+- Added `id` field as secondary sort to sort config to ensure unique pagination tokens. [#421](https://github.com/stac-utils/stac-fastapi-elasticsearch-opensearch/pull/421)
+
 
 ## [v6.2.0] - 2025-08-27