DOC: Include new notebooks in .rst docs

[david-cortes-intel]

Description

ref #2343

The PR above introduced new notebooks showcasing speedups of sklearnex.

All of these notebooks get copied automatically into the docs folder from where the .rst files include them. Since our docs build logic is to turn all warnings into errors, this currently leads to errors like these:

checking consistency... /home/vsts/work/1/s/doc/sources/samples/random_forest_rain.ipynb: WARNING: document isn't included in any toctree [toc.not_included]
/home/vsts/work/1/s/doc/sources/samples/ridge_regression_bike_sharing.ipynb: WARNING: document isn't included in any toctree [toc.not_included]
/home/vsts/work/1/s/doc/sources/samples/ridge_regression_fraud_detection.ipynb: WARNING: document isn't included in any toctree [toc.not_included]
/home/vsts/work/1/s/doc/sources/samples/ridge_regression_higgs.ipynb: WARNING: document isn't included in any toctree [toc.not_included]

This PR fixes them by including these new notebooks in the relevant .rst files.

---

PR should start as a draft, then move to ready for review state after CI is passed and all applicable checkboxes are closed.
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Checklist to comply with before moving PR from draft:

PR completeness and readability

• I have reviewed my changes thoroughly before submitting this pull request.
• I have updated the documentation to reflect the changes or created a separate PR with update and provided its number in the description, if necessary.
• Git commit message contains an appropriate signed-off-by string (see CONTRIBUTING.md for details).
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Testing

• I have run it locally and tested the changes extensively.
• All CI jobs are green or I have provided justification why they aren't.

Performance

Not applicable.

[david-cortes-intel]

Screenshot of new inclusions in generated artifact:

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

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