Switch to Plone Sphinx Theme for documentation, include changes to http-examples to build docs preview

[stevepiercy]

• Switch to Plone Sphinx Theme for documentation
• The http-examples directory is now included for pull request previews.
• I resynced the RTD webhook in this repo's settings as the PR preview builds were failing.

Closes #1097

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📚 Documentation preview 📚: https://plonerestapi--1815.org.readthedocs.build/

[mister-roboto]

@stevepiercy thanks for creating this Pull Request and helping to improve Plone!

TL;DR: Finish pushing changes, pass all other checks, then paste a comment:

@jenkins-plone-org please run jobs

To ensure that these changes do not break other parts of Plone, the Plone test suite matrix needs to pass, but it takes 30-60 min. Other CI checks are usually much faster and the Plone Jenkins resources are limited, so when done pushing changes and all other checks pass either start all Jenkins PR jobs yourself, or simply add the comment above in this PR to start all the jobs automatically.

Happy hacking!

[stevepiercy]

@jenkins-plone-org please run jobs

[stevepiercy]

There are two issues with the theme, which I can resolve in a future pull request, as this is an improvement.

1. The tabs for http-examples have a white background in both light and dark mode, but should adapt.
2. ScrollSpy is not working on the right-hand in-page navigation.

[wesleybl]

The tabs for http-examples have a white background in both light and dark mode, but should adapt.

This really looks weird, no contrast. It really needs to be fixed.

[stevepiercy]

The tabs for http-examples have a white background in both light and dark mode, but should adapt.

This really looks weird, no contrast. It really needs to be fixed.

This should be fixed in PST 0.0.15. Preview: https://plonerestapi--1815.org.readthedocs.build/en/1815/endpoints/aliases.html#adding-new-url-aliases-for-a-page

[stevepiercy]

The ScrollSpy bug is weird. Something in this repo interferes with it, as it is fine in the PST docs. If anyone can spy the issue, I'd appreciate the assist.

[stevepiercy]

@jenkins-plone-org please run jobs

[stevepiercy]

I'm not sure why the one Jenkins run fails, as this PR has nothing to do with its failing tests.