Move versions inside public directory instead the other way around

The latest MR !520 (merged) doesn't quite work in production when the Docker images with all versions is used https://gitlab.com/gitlab-org/gitlab-docs/-/jobs/277325482:

$ mv public latest
$ mv /usr/share/nginx/html public
$ cp -a latest/* public/
cp: can't create 'public/ce': File exists

This change attempts to fix that by changing how Pages deployment works.