[v11.4.x] Docs: Add 11.4 to supported versions table (#98773)

Co-authored-by: Zach Day <zachary.day@grafana.com>

docs/sources/upgrade-guide/when-to-upgrade/index.md

@@ -94,6 +94,7 @@ Here is an overview of projected version support through 2024:
 | 11.1                      | June 2024        | March 2025                             |
 | 11.2                      | August 2024      | May 2025                               |
 | 11.3                      | October 2024     | July 2025                              |
+| 11.4                      | December 2024    | September 2025                         |
 
 {{< admonition type="note" >}}
 Grafana 9.5.x was the last supported minor for the 9.0 major release and is no longer supported as of July 2024.