Simplify HTML rendering build process #3852

Currently, to build the HTML versions of the spec, you need to simulate .github/workflows/respec.yam by doing (in the root of a checked-out main branch of the repository):

1. make sure you have node version 20 installed
2. npm install
3. ./scripts/md2html/build.sh
4. git checkout gh-pages
5. cp -R js deploy/js

Then you can look at the rendered HTML. After the first time you only have to do the ./scripts/md2html/build.sh (from main).

If you need to render a new version of the spec, you also need to add a new MAINTAINERS_vX.Y.Z.md file in the scripts/md2html/history directory (which the error message you get will show as ./history).

We should fix this as we fix #3717, #3845, and #3715.