Should we-organize our GitHub pages to a directory on main?

[handrews]

Splitting this out from #3766, to which it is still somewhat related as we should consider the impact on how many PRs to how many different branches are required for a change that spans the spec and the registries.

Originally, gh-pages sites needed to be on a gh-pages branch that (as ours does) typically has a completely different layout than main. That is no longer required, and it is much more common to deploy from a directory on main. Or at least from a directory on a branch that is no more different from main than any other working branch.

[Bellangelo]

I totally agree with this one. This might be a personal preference but I usually find it confusing when each branch is a different project completely. I can start with this one after this is closed #1823

[handrews]

Note that the current build process seems spread across both main and gh-pages, plus duplication for the OAS and Arazzo specs, which probably needs to be unraveled.

Also, there are infrastructure bits under the curren top-level directory on main which should probably be pushed down into the directory that will replace the gh-pages branch to reduce clutter.