code: @Controller(events = EventType.FILE_SHARED)
      public void onFileShared(WebSocketSession session, Event event) {
          logger.info("File shared: {}", event);
      }
docs: Invoked when bot receives an event of type file shared.
  NOTE: You can't reply to this event as slack doesn't send
  a channel id for this event type. You can learn more about
  <a href="https://api.slack.com/events/file_shared">file_shared</a>
  event from Slack's Api documentation.
  
  @param session
  @param event