Add 12 hour clock device display config

meshtastic/config.proto

@@ -743,6 +743,12 @@ message Config {
      * Indicates how to rotate or invert the compass output to accurate display on the display.
      */
     CompassOrientation compass_orientation = 11;
+
+    /*
+     * If false (default), the device will display the time in 24-hour format on screen.
+     * If true, the device will display the time in 12-hour format on screen.
+     */
+    bool use_12h_clock = 12;
   }
 
   /*