Add support for GPT-4 16k and 32k

I can do this, just making an issue for me to add in the future :) 

Task: add support for GPT-3.5 16k and GPT-4 32k to allow for more context, especially for large webpages and those running into context issues: https://platform.openai.com/docs/models/overview

https://github.com/TaxyAI/browser-extension/blob/dcb244fd89a5ec2f6345b61facd51fca8da3c1f5/src/common/ModelDropdown.tsx#L25