chore: add changelog entry

Author: 43081j

CHANGELOG.md

@@ -11,6 +11,7 @@ For notes on migrating to 2.x / 0.200.x see [the upgrade guide](doc/upgrade-to-2
 ## Unreleased
 
 * feat(instrumentation-http): Added support for redacting specific url query string values and url credentials in instrumentations [#5743](https://github.com/open-telemetry/opentelemetry-js/pull/5743) @rads-1996
+* perf(opentelemetry-core): optimize attribute serialization [#5866](https://github.com/open-telemetry/opentelemetry-js/pull/5866) @43081j
 
 ### :boom: Breaking Changes