Add support for Azure, Palm, Anthropic, Cohere, Hugging Face Llama2 70b Models - using litellm

[ishaan-jaff]

This PR adds support for models from all the above mentioned providers using https://github.com/BerriAI/litellm/

All LLM API Models are guaranteed to have the same Input/Output interface

Here's a sample of how it's used:

from litellm import completion

## set ENV variables
# ENV variables can be set in .env file, too. Example in .env.example
os.environ["OPENAI_API_KEY"] = "openai key"
os.environ["COHERE_API_KEY"] = "cohere key"
os.environ["HF_API_TOKEN"] = "hf-key"

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

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

# hugging face llama2 call
completion(model="meta-llama/llama-2-7b-hf", messages=messages)

# hugging face llama2 Guanaco call
completion(model="TheBloke/llama-2-70b-Guanaco-QLoRA-fp16", messages=messages)

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

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

[ishaan-jaff]

@KamilPiechowiak @janchorowski can you please take a look at this PR ?😊

Happy to add more docs / testing if this initial commit looks good

[janchorowski]

Many thanks @ishaan-jaff! We are finalizing the process for accepting contributions, I'm OOO until Wednesday and then will review your PR.

[CLAassistant]

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[janchorowski]

Closing due to inactivity.