notebooks: align notebook inclusion + testing with upstream repos

Description

The rapidsai/notebooks image bundles sample notebooks from a few RAPIDS projects.

CI here tests them:

https://github.com/rapidsai/docker/blob/3a8d371dbaa28acc9148ed80ac292b12ff2d63c1/.github/workflows/test-notebooks.yml#L93-L94

CI here often fails a few times a release with problems of the form "some notebook broke upstream and isn't tested in CI there but is here".

That problem should be engineered away.

Benefits of this work

• improved CI stability
• improved release confidence
• reduced maintenance burden

Acceptance Criteria

• there are 0 notebooks tested in this project's CI which aren't tested in the repo where they're developed

Approach

I can see a few differnent ways to do this, listing some ideas here:

• ensure all the notebooks are tested in the cuDF, cuML, cuGraph, etc. repos
• stop testing any notebooks here and accept them as-is
• stop bundling notebooks in these images at all (then rapidsai/notebooks would become "rapidsai/base + a jupyterlab setup)
• somehow programatically align what's tested here with what's tested in the repos (like invoking a test_notebooks.sh script directly from the repos or something)

Notes

N/A

Start with .github/workflows/test-notebooks.yml around lines 93-94 and inspect how this repository selects and tests notebooks. Compare that set with the corresponding testing entry points in the RAPIDS repositories that develop them. Done means no notebook is tested here unless it is also tested in its development repository.