[FR] Resent the incoming photo as a file

When the flag `send_image_as_file` is false, users reply to an incoming photo message with `/resent` command, ETM will reply to the selected message (Easy to trace back), then resent that photo as a file to the session. Or return an error if the message id got invalid due to EWS session refresh.

When the flag is true, ETM should ignore the `/resent` command, or return a error.

当ETM属性 `send_image_as_file` 为false时响应 `/resent` 指令，用户发送指令回复一条bot转发的图片消息，ETM会引用该消息（方便回溯定位）并将该图片以文件形式重新发到会话中。若EWS会话刷新导致该消息id失效则返回报错。
若上述ETM属性为true则不响应 `/resent` 命令或返回错误。