add missing changelog entry to 2.13 release nodes (#12851)

Signed-off-by: Varun Bansal <bansvaru@amazon.com>

Author: linuxpi

release-notes/opensearch.release-notes-2.13.0.md

@@ -26,6 +26,7 @@
 - Add Remote Store Migration Experimental flag and allow mixed mode clusters under same ([#11986](https://github.com/opensearch-project/OpenSearch/pull/11986))
 - Built-in secure transports support ([#12435](https://github.com/opensearch-project/OpenSearch/pull/12435))
 - Lightweight Transport action to verify local term before fetching cluster-state from remote ([#12252](https://github.com/opensearch-project/OpenSearch/pull/12252/))
+- Integrate with admission controller for cluster-manager Read API. ([#12496](https://github.com/opensearch-project/OpenSearch/pull/12496))
 
 ### Dependencies
 - Bump `com.squareup.okio:okio` from 3.7.0 to 3.8.0 ([#12290](https://github.com/opensearch-project/OpenSearch/pull/12290))