Feat: Use a local GPT2 model as a fallback.

[lychees]

OpenAI is currently facing tremendous traffic, making the ChatGPT service often unavailable. There are other NLP model, e.g. GPT2 which is open-source and easy to get via the internet, can we add a fallback function so that when the connection is broken, the bot can still responding to user's input.

[MaikoTan]

I don't think this is a good solution. This would not only break our conversation context maintaining state, but also makes the conversation unstable (as you see the GPT2 model you mentioned always behaves bad compare to ChatGPT).