Add Connectors release notes for 8.18

Author: charlotte-hoblik

docs/reference/connector/docs/connectors-release-notes.asciidoc

@@ -9,6 +9,18 @@
 Prior to version *8.16.0*, the connector release notes were published as part of the {enterprise-search-ref}/changelog.html[Enterprise Search documentation].
 ====
 
+[discrete]
+[[es-connectors-release-notes-8-18-2]]
+=== 8.18.2
+
+No notable changes in this release.
+
+[discrete]
+[[es-connectors-release-notes-8-18-1]]
+=== 8.18.1
+
+No notable changes in this release.
+
 [discrete]
 [[es-connectors-release-notes-8-18-0]]
 === 8.18.0