Update CHANGELOG

Signed-off-by: Atri Sharma <[email protected]>

Author: atris

CHANGELOG.md

@@ -5,6 +5,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 
 ## [Unreleased 3.x]
 ### Added
+- Add hierarchical routing processors for ingest and search pipelines ([#18826](https://github.com/opensearch-project/OpenSearch/pull/18826))
 - Add support for Warm Indices Write Block on Flood Watermark breach ([#18375](https://github.com/opensearch-project/OpenSearch/pull/18375))
 - FS stats for warm nodes based on addressable space ([#18767](https://github.com/opensearch-project/OpenSearch/pull/18767))
 - Add support for custom index name resolver from cluster plugin ([#18593](https://github.com/opensearch-project/OpenSearch/pull/18593))