Release notes for 8.18.6 (#18048)

* Update release notes for 8.18.6

* curate release notes

---------

Co-authored-by: logstashmachine <[email protected]>
Co-authored-by: donoghuc <[email protected]>

Author: 3 people

docs/static/releasenotes.asciidoc

@@ -3,6 +3,7 @@
 
 This section summarizes the changes in the following releases:
 
+* <<logstash-8-18-6,Logstash 8.18.6>>
 * <<logstash-8-18-5,Logstash 8.18.5>>
 * <<logstash-8-18-4,Logstash 8.18.4>>
 * <<logstash-8-18-3,Logstash 8.18.3>>
@@ -92,6 +93,15 @@ This section summarizes the changes in the following releases:
 * <<logstash-8-0-0-alpha2,Logstash 8.0.0-alpha2>>
 * <<logstash-8-0-0-alpha1,Logstash 8.0.0-alpha1>>
 
+[[logstash-8-18-6]]
+=== Logstash 8.18.6 Release Notes
+
+No user-facing changes in Logstash core.
+
+==== Plugins
+
+No change to the plugins in this release.
+
 [[logstash-8-18-5]]
 === Logstash 8.18.5 Release Notes