Add LangChain recipes

[rlancemartin]

What does this PR do?

Add recipes for LangChain agents.

Feature/Issue validation/testing

Notebooks tested in fresh conda env.

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[jeffxtang]

@rlancemartin
Thanks for the PR Lance! I made and pushed some changes (summary in the commit message) to the 4 notebooks and will continue to play with it later. I noticed in the tool-calling-agent notebook, using app.invoke({"question":"What is LangSmith?"}) would return correct result. In the local notebook, the answer to "What are the types of agent memory?" is not as good as the non-local Groq's llama 3 70b based one.

Please take a look at my changes and let me know what you think. I'll see if it's possible to simplify langgraph-agent to make the benefits of using LG over AE obvious.

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