[Observability] Add Observability 9.1.4 release notes (#2896)

This PR closes #2860

Co-authored-by: florent-leborgne <[email protected]>

Author: mdbirnstiehl

release-notes/elastic-observability/index.md

@@ -21,6 +21,13 @@ To check for security updates, go to [Security announcements for the Elastic sta
 % ### Fixes [elastic-observability-next-fixes]
 % *
 
+## 9.1.4 [elastic-observability-9.1.4-release-notes]
+
+### Enhancements [elastic-observability-9.1.4-enhancements]
+
+* Save button is disabled in user-specific system prompt flyout when there's no input [#231562]({{kib-pull}}2301562).
+
+
 ## 9.1.3 [elastic-observability-9.1.3-release-notes]
 
 ### Fixes [elastic-observability-9.1.3-fixes]