Extend duration documentation about frequenz-api-dispatch HOT 4 OPEN

message Dispatch {
  // ...

-  // Duration in seconds
+  // Duration of the dispatch in seconds. 
+  //
+  // The duration specifies how long each occurrence of the dispatch lasts during 
+  // a single run, applies only to the individual instance and not the overall cycle of 
+  // recurring dispatches. This setting is independent of the recurrence pattern, 
+  // which is governed by separate recurrence settings.
+  // 
+  // !!! note
+  //     This field manages how long each occurrence of the dispatch lasts:
+  //     - `null` value indicates an infinite duration, meaning each dispatch occurrence 
+  //.      continues indefinitely.
+  //     - A value of `0` indicates a one-time execution for that particular occurrence, 
+  //       which does not repeat or persist beyond its initial run.
+  //     - Positive values specify the duration in seconds for each dispatch occurrence 
+  //       should be active.
+  //
+  //     Example of how to set duration
+  //         duration_seconds: { value: 3600 } // Duration of 1 hour
+  //         duration_seconds: null // Infinite duration
+  //         duration_seconds: { value: 0 } // One-time execution    
+  //
- //    uint32 duration = 7;
+ //  optional uint32 duration_seconds = 7;
}