Support changing model for chatgpt-browser

[wind2sing]

According to waylaidwanderer/node-chatgpt-api #using-a-reverse-proxy, we can set the model to text-davinci-002-render, text-davinci-002-render-paid, or text-davinci-002-render-sha depending on which ChatGPT models that your account has access to.

By looking at the response body for https://chat.openai.com/backend-api/models, currently we have three types of models for ChatGPT-plus users.

Perhaps we could use an environment variable to set the type of model for chatgpt-browser.

[danny-avila]

you're right and that would be pretty simple to implement. i can include this in the next update through an env var

[danny-avila]

Addressed in latest release #117 @wind2sing