Add support for JSON mode

[shinohara-rin]

OpenAI recently introduced a new feature called JSON mode

I didn't see anyone working on this, so I've take the liberty to implement the new parameter response_format.

It works with a fresh instance of BetterChatGPT. However, I had no luck on migrating from previous versions. For now you probably need to manually set the field if you are upgrading from previous versions

I'll be thankful if someone can help me with the migration problem.

[animalnots]

provided you got it saving similar to other props (e.g. max_tokens) this should work

export const migrateV8 = (persistedState: LocalStorageInterfaceV8toV9) => {
 persistedState.chats.forEach((chat) => {
    chat.config = {
      ...chat.config,
      responseFormat : defaultResponseFormat,
    };
  });
}

I would rename responseFormat to response_format for consistency purposes