Add changelog

Author: DylanRussell

instrumentation-genai/opentelemetry-instrumentation-openai-v2/CHANGELOG.md

@@ -9,6 +9,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Record prompt and completion events regardless of span sampling decision.
   ([#3226](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/3226))
+- Migrate off the deprecated events API to use the logs API
+  ([#3625](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/3628))
 
 ## Version 2.1b0 (2025-01-18)