[8.19] (backport #285) Update CHANGELOG.md for 8.18.0 (#289)

Author: mergify[bot]

CHANGELOG.md

@@ -1,3 +1,7 @@
+## 8.18.0
+  - Aligns with stack major and minor versions, no functional changes [#285](https://github.com/elastic/logstash-filter-elastic_integration/pull/285)
+  - Embeds Ingest Node components from Elasticsearch 8.18
+  
 ## 8.17.1
   - Provides a guidance in logs when plugin version mismatches with connected Elasticsearch `major.minor` version [#255](https://github.com/elastic/logstash-filter-elastic_integration/pull/255)
   - Embeds Ingest Node components from Elasticsearch 8.17