Update notification response message for clarity

- Changed the response message in the `Send` method of the `NotificationHandler` from "Notification sent successfully" to "Notification created successfully" to better reflect the action performed.

This update improves the clarity of the notification response, ensuring users receive accurate feedback on their actions.

internal/notification/handler.go

@@ -49,7 +49,7 @@ func (h *NotificationHandler) Send(c echo.Context) error {
 	// Send notification
 	go h.service.Send(context.Background(), &req)
 
-	return response.Created(c, nil, "Notification sent successfully")
+	return response.Created(c, nil, "Notification created successfully")
 }
 
 // GetNotifications gets notifications