update changelog

Author: etserend

util/opentelemetry-util-genai/CHANGELOG.md

@@ -7,6 +7,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## Unreleased
 
+- Add `AgentInvocation` type and agent invocation lifecycle support
+  ([#4274](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/4274))
 - Add support for emitting inference events and enrich message types. ([#3994](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/3994))
 - Add support for `server.address`, `server.port` on all signals and additional metric-only attributes
   ([#4069](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/4069))