[Feat]: 私聊中，Ai回复可选加前缀

[Ethan-Ming]

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Feature description

有些时候希望能让对方区分出是我还是Ai在回复他

Motivation

No response

[q735409242]

wechat.py里build_msg函数的content加上你要的前缀就可以了

[QAbot-zh]

https://github.com/iuiaoin/wechat-gptbot/pull/71#issue-1828482249 简单实现了一下

[iuiaoin]

Done with #74