docs(website): add the tutorial using scikit-learn

[deepyaman]

In preparation for adding a framework picker on the website, we need to convert the tutorial to Quarto (ipywidgets pickers don't work for interactive execution).

Also, standardize on level 2 headings (including in the notebook), and make other minor improvements (quote standardization, whitespace removal, etc.).

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 84.53%. Comparing base (92a4a23) to head (cbdc3c4). Report is 21 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #111 +/- ## ======================================= Coverage 84.53% 84.53% ======================================= Files 24 24 Lines 1862 1862 ======================================= Hits 1574 1574 Misses 288 288 ```

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