Rebuilding langchain-retrieval-agent notebook to use LangGraph and Assistant (#464)

## Problem

Describe the purpose of this change. What problem is being solved and
why?

Replacing broken notebook using langchain to instead be using LangGraph
and Assistant. Gives us coverage across all aspects of Pinecone in the
examples page now!

## Solution

Describe the approach you took. Link to any relevant bugs, issues, docs,
or other resources.

## Type of Change

- [ ] Bug fix (non-breaking change which fixes an issue)
- [ ] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing
functionality to not work as expected)
- [ ] This change requires a documentation update
- [ ] Infrastructure change (CI configs, etc)
- [ ] Non-code change (docs, etc)
- [ ] None of the above: (explain here)

## Test Plan

Describe specific steps for validating this change.


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used, see below:
  - https://app.asana.com/0/0/1210173857372759

Author: arjunpatel7