Release notes for 8.18.8 (#18245)

* Update release notes for 8.18.8

* finalize release notes

* Update docs/static/releasenotes.asciidoc

Co-authored-by: Karen Metts <[email protected]>

---------

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

Author: 4 people

docs/static/releasenotes.asciidoc

@@ -3,6 +3,7 @@
 
 This section summarizes the changes in the following releases:
 
+* <<logstash-8-18-8,Logstash 8.18.8>>
 * <<logstash-8-18-7,Logstash 8.18.7>>
 * <<logstash-8-18-6,Logstash 8.18.6>>
 * <<logstash-8-18-5,Logstash 8.18.5>>
@@ -94,6 +95,16 @@ 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-8-18-8]]
+=== Logstash 8.18.8 Release Notes
+
+No user-facing changes in Logstash core.
+
+[[plugins-8-18-8]]
+==== Plugins
+
+No user-facing changes. 
+
 [[logstash-8-18-7]]
 === Logstash 8.18.7 Release Notes