Find way to avoid need for docs/conf.yaml version maintenance per-project

Now that project-specific docs have moved out of the docs project and to individual projects, each project has a docs/conf.yaml with a version name that needs to match the branch (Neon for master at the moment, Fluorine for stable/fluorine, etc). It's not great to have to manually do this for all the projects. Maybe we can pull it from a central place, or at least add some scripting/automation. Should also doc/handle this is in the normal branch cutting process.