How to update our documentation to remove /en/latest and to use clean urls instead of ones with .html without breaking links

[choldgraf]

@consideRatio recently figured out a way to do two things in a way that don’t break URLs:

1. Remove /en/latest from Sphinx documentation (for docs where we don’t intend to version or localize the content)
2. Remove .html from webpages so that they have “clean URLs” (e.g. page/ rather than page.html)

We wrote it up as a brief team guide in case it’s useful to others. Sharing here for visibility:

[Team guide] How to update our documentation to remove `/en/latest` and to use `clean urls` instead of ones with `.html` without breaking links