Add connectors release notes (#134773)

Author: charlotte-hoblik

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

@@ -9,6 +9,17 @@
 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-8-19-4]]
+=== 8.19.4
+
+[discrete]
+[[es-connectors-release-notes-8-19-4-enhancements]]
+==== Enhancements
+
+* Salesforce connector: Reduced API calls during field validation with caching, improving sync performance.
+See https://github.com/elastic/connectors/pull/3668[*PR 3668*].
+
 [discrete]
 [[es-connectors-release-notes-8-19-3]]
 === 8.19.3