Update CHANGELOG.md - add date

Author: jonhealy1

CHANGELOG.md

@@ -13,7 +13,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 ### Fixed
 
-## [v4.0.0a0]
+## [v4.0.0a0] - 2025-04-17
 
 ### Added
 - Added support for dynamically-generated queryables based on Elasticsearch/OpenSearch mappings, with extensible metadata augmentation [#351](https://github.com/stac-utils/stac-fastapi-elasticsearch-opensearch/pull/351)