Adds LangChain translation example

[rachfop]

What was changed

Add an example of LangChain.

Why?

Checklist

1. Closes

I need help with Poetry and a Pydantic Converter.

I tried setting the dev dependencies like this, so I wouldn't have to change the top-level version - but that didn't work.
So I just overwrote the Python dependcy.

dependencies = { langchain = { version = "^0.0.350", python = ">=3.8.1,<4.0" }, openai = { version = "^1.4.0", python = ">=3.8,<4.0" }, fastapi = { version="^0.105.0", python = ">=3.8,<4.0"}, uvicorn = { version = "^0.24.0.post1", extras = ["standard"], python = ">=3.8,<4.0" } }

While this code works, it probably needs a Pydantic Convert for V2 to properly serialize.

3. How was this tested:

4. Any docs updates needed?