Ability to pick a (non-current) version to redirect to

[mchristofides]

Thinking about a settings menu with this as an option.

Use cases that I believe exist:

• currently doing a big migration to a (now) non-current release, and cannot consider an upgrade at this point
• working with a legacy (or military, or regulated) application that doesn't support the latest versions
• PostgreSQL contributor, and would like to see "devel" docs by default

Do comment on this if you'd like it, ideally with your version number and use case!

Update: There is a new extension, Unified Docs Switcher that may be a better fit for folks who want a different default version!