Clean up

[brian-rose]

A bunch of clean-up to the Template prior to the 2023 hackathon:

• Point all Binder links to the new Pythia binder at https://binder.projectpythia.org
• Updates to pre-commit hooks
• Formatting fixes from running pre-commit locally
• Update copyright year
• Add a few more helpful comments in the _config file

To address #119 I plan to switch on the pre-commit.ci service for this repo to keep this stuff up to date in the template, but leave it as completely optional for individual cookbooks.

[github-actions]

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[brian-rose]

As a few of the infrastructure folks discussed today, this PR also preserves the default option of executing notebooks on GitHub Actions. We will switch individual cookbooks over to building on the Binder on an as-needed basis.

However the Pythia Binder is now the default platform for interactive use of the Cookbooks, even for Cookbooks that don't run their nightly builds on the Binder.