docs/reference/matrix.rst: add the unstable 4.9 version

(cherry picked from commit eeb684e)

Author: amnonh

docs/source/reference/matrix.rst

@@ -14,6 +14,11 @@ The following table shows which version of Scylla Monitoring Stack supports dash
      - Scylla Enterprise Version
      - Node_exporter[1] Version
      - Scylla Manager Version
+   * - 4.9
+     - 6.0, 6.1, 6.2
+     - 2022.2, 2023.1, 2024.1, 2024.2, 2025.1
+     - 1.7.0
+     - 3.4
    * - 4.8
      - 5.2, 5.4, 6.0, 6.1
      - 2022.1, 2022.2, 2023.1, 2024.1, 2024.2