Implement receive_notification function in Notification service.

src/service/notification.rs

@@ -83,4 +83,8 @@ impl NotificationService{
         return thread::spawn(move || Self::unsubscribe_request(product_type_clone)).join().unwrap();
     }
 
+    pub fn receive_notification(payload: Notification) -> Result<Notification> {
+        let subscriber_result: Notification = NotificationRepository::add(payload);
+        return Ok(subscriber_result);
+    }
 }
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