add support for anthropic, bedrock, azure, ai21, cohere, replicate, togetherai, etc.

[krrishdholakia]

Hi @GokuMohandas @pcmoritz,

Noticed you're calling the openai chat completions endpoint. I'm working on litellm (simple library to standardize LLM API Calls - https://github.com/BerriAI/litellm) and wanted to see how i could be helpful.

My PR adds support for new LLM providers (anthropic, aws bedrock, azure openai, replicate, ai21, etc.) by replacing openai's http ChatCompletion with litellm.completion.

Curious if you find this useful?

Happy to add additional tests/documentation if the initial PR looks good.