Merge PRs on GLM-robust notebook

[OriolAbril]

• Notebook follows style guide https://docs.pymc.io/en/latest/contributing/jupyter_style.html
• PR description contains a link to the relevant issue: closes notebook: GLM-robust-regression #435 and closes GLM robust #88
• Check the notebook is not excluded from any pre-commit check: https://github.com/pymc-devs/pymc-examples/blob/main/.pre-commit-config.yaml

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[OriolAbril]

I think I kept all relevant work. This supersedes #356, #445, #451. I'll go close them now

[reshamas]

Thanks @OriolAbril! And apologies you had to integrate 3 separate PRs to get this one in!