Added a demonstartion notebook featuring the usage of Langchain with …

…AutoGen (#3461)

* Added langchain integrated demo  notebook

* Added output

* Update notebook/agentchat_huggingface_langchain.ipynb

Co-authored-by: gagb <[email protected]>

* Changed the underlying LLM and lint fix

* lint fix

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Co-authored-by: gagb <[email protected]>
Co-authored-by: HRUSHIKESH DOKALA <[email protected]>
Co-authored-by: Eric Zhu <[email protected]>