Add support for Llama2, Palm, Cohere, Anthropic, Replicate, Azure Mod…

…els - using litellm (#13)

This PR adds support for 50+ models with a standard I/O interface using:
https://github.com/BerriAI/litellm/

`ChatLiteLLM()` is integrated into langchain and allows you to call all
models using the `ChatOpenAI` I/O interface
https://python.langchain.com/docs/integrations/chat/litellm

Here's an example of how to use ChatLiteLLM()
```python
ChatLiteLLM(model="gpt-3.5-turbo")
ChatLiteLLM(model="claude-2", temperature=0.3)
ChatLiteLLM(model="command-nightly")
ChatLiteLLM(model="replicate/llama-2-70b-chat:2c1608e18606fad2812020dc541930f2d0495ce32eee50074220b87300bc16e1")

```

---------

Co-authored-by: fynnfluegge <fynnfluegge@gmx.de>

doc_comments_ai/llm.py

@@ -5,7 +5,7 @@
 
 import inquirer
 from langchain import LLMChain, PromptTemplate
-from langchain.chat_models import ChatOpenAI
+from langchain.chat_models import ChatLiteLLM
 from langchain.llms import LlamaCpp
 
 from doc_comments_ai import utils
@@ -33,7 +33,7 @@ def __init__(
                 verbose=False,
             )
         else:
-            self.llm = ChatOpenAI(
+            self.llm = ChatLiteLLM(
                 temperature=0.9, max_tokens=max_tokens, model=model.value
             )
         self.template = (