Add support for Claude-2, Cohere Llama2, CodeLlama, Azure OpenAI, Replicate LLMs (100+LLMs)

[ishaan-jaff]

This PR adds support for the above mentioned LLMs using LiteLLM https://github.com/BerriAI/litellm/ LiteLLM is a lightweight package to simplify LLM API calls - use any llm as a drop in replacement for gpt-3.5-turbo.

Example

from litellm import completion

## set ENV variables
os.environ["OPENAI_API_KEY"] = "openai key"
os.environ["COHERE_API_KEY"] = "cohere key"

messages = [{ "content": "Hello, how are you?","role": "user"}]

# openai call
response = completion(model="gpt-3.5-turbo", messages=messages)

# cohere call
response = completion(model="command-nightly", messages)

# anthropic call
response = completion(model="claude-instant-1", messages=messages)

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[ishaan-jaff]

@pablohashescobar @vihar can i get a review on this PR ?

happy to add docs/tests if this initial commit looks good

[krrishdholakia]

bump on this? @Palanikannan1437 @aaryan610 @pablohashescobar

[sriramveeraghanta]

Dear @ishaan-jaff and @krrishdholakia,

We are developing a novel approach to enhance our platform by integrating additional AI engines. This improves the overall integration process and provides a more seamless experience.

[CLAassistant]

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[pablohashescobar]

@ishaan-jaff, thank you for contributing to Plane. We will be merging this PR.