Remake gen-qa-openai notebook with new dataset, and cascading retrieval (#462)

## Problem

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

Old docs notebook was outdated and used a dataset with old embedding
models.

## Solution

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

New docs notebook uses openai model for generation, cascading retrieval
and integrated inference for querying.

## 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.


---
- To see the specific tasks where the Asana app for GitHub is being
used, see below:
  - https://app.asana.com/0/0/1210173857372766

Author: arjunpatel7