Add support for Llama2, Palm, Cohere, Replicate Models - using litellm

[ishaan-jaff]

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

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

from litellm import completion, acompletion

## 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"

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

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

# llama2 call
model_name = "replicate/llama-2-70b-chat:2c1608e18606fad2812020dc541930f2d0495ce32eee50074220b87300bc16e1"
response = completion(model_name, messages)

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

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

[ishaan-jaff]

@riverscuomo can you take a look at this pr when possible?

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

[riverscuomo]

This is cool, thank you.
Let me ask a few questions to help me understand the purpose of the PR:

• Are you thinking that we may end up using some of the other services, like Llama2?
• Should I use litellm.completion for my existing Replicate calls too?

[ishaan-jaff]

@riverscuomo

Are you thinking that we may end up using some of the other services, like Llama2?

This is your call - we support all LLM providers and models. so you can start using any service you'd like in the future

Should I use litellm.completion for my existing Replicate calls too?

Yes, docs on this is here: https://docs.litellm.ai/docs/providers/replicate