Add 404 handler that redirects to www.drupal.org

Problem/Motivation

drupalorg is now doing a pretty good job of only serving what we are ready to serve, except 404s that are real pages on the legacy site.

A 404 handler that redirects to www.drupal.org seems like a good idea. Except that we also want the legacy site to handle its own redirects to new.drupal.org without the CDN configuration. That can’t be a 404 handler too, legitimate 404s would infinite redirect.

We’ll need one of the sites to test the other before redirecting, and cache the result. And/or keep some amount of path-based redirects, in a Drupal codebase for maintainability.

Proposed resolution

Add 404 handler to new.drupal.org that either redirects to the same request on www.drupal.org or that tests that it exists and then either redirect or throw a 404.