Migration of git-scm.com to a static web site: ready for review/testing

Hi,

the idea of migrating https://git-scm.com/ from a Rails app to a static site has been discussed several times on this list in the past.

Thanks to the heroic, multi-year efforts of Matt Burke, Victoria Dye and Matthias Aßhauer, there is now a Pull Request, ready for review: https://github.com/git/git-scm.com/pull/1804

This Pull Request is not for the faint of heart, mainly because of the sheer amount of generated pages that are committed to the repository (such as the book, the manual pages, etc, a design decision necessary to run this as a static website).

These pages are generated by GitHub workflows that are intended to run on a schedule, and the scripts that generate them are part of the Pull Request. For that reason, I do not consider it necessary to review those generated pages, those reviews have been done in the upstream sources from which the pages were generated.

At this point, the patches are fairly robust and I am mainly hoping for help with verifying that the static site works as intended, that existing links will continue to work with the new site (essentially, find obscure references to the existing website, then insert `git.github.io/` in the URL and verify that it works as intended).

To that end, I deployed this branch to GitHub Pages so that anyone interested (hopefully many!) can have a look at https://git.github.io/git-scm.com/ and compare to the existing https://git-scm.com/.

Thank you, Johannes