Add impersonate feature to API /v1/chat/completions

[Yiximail]

The feature same as the impersonate feature on webui.

Add an impersonate param to active this feature in /v1/chat/completions.

Updated:
Prepend user_input in impersonate reply for consistency
It will always returns the entire message now

Checklist:

• I have read the Contributing guidelines.

Test Images

Impersonate:

Normal response:

[Yiximail]

Is there something wrong with it...? You can tell me, and I can fix it
Sorry for the mention @oobabooga

I use this quite often in api.
I just updated the webui today and realized that it wasn't merged.

[jianmomo]

Is there something wrong with it...? You can tell me, and I can fix it Sorry for the mention @oobabooga

I use this quite often in api. I just updated the webui today and realized that it wasn't merged.
I'm not sure what issues there might be with my modifications.
I directly copied the contents of typing.py and completions.py, and added a parameter for mimicry in the request. However, there's a problem with the responses—they always start with "ai...".

[Yiximail]

Is there something wrong with it...? You can tell me, and I can fix it Sorry for the mention @oobabooga
I use this quite often in api. I just updated the webui today and realized that it wasn't merged.
I'm not sure what issues there might be with my modifications.
I directly copied the contents of typing.py and completions.py, and added a parameter for mimicry in the request. However, there's a problem with the responses—they always start with "ai...".

咳咳，这图不合适吧

请提供一下你的模型，和完整prompt（运行的时候加上 --verbose 参数) 带上seed更好

一般这个commit不影响生成内容才对，只是处理了一下让它不会创建新的assistant对话，而是接着在user的content中续写补充

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啊，我知道了，这是chat模式的bug

设置了 bot_name 但是没生效

它读取的依然是默认的 Assistant 角色卡 的内容，bot_name 没覆盖它
那和这个commit没什么关系啦，不一起改了

（好少用chat模式……）

[jianmomo]

OK, thank you. It seems that I need to learn the framework code carefully. Thank you very much for your help.