support for openai endpoint models

[JINO-ROHIT]

it would be nice to support more model providers specifically openai models. this would also open up the possibilities to run local models with an openai compatible api.

[will-fawcett-trillium]

Work in progress: #7
Step one is to allow for providers from OpenAI and Anthropic (as well as google) as well as allowing for model choice.