sitemap should not return an empty file if indexing isn't configured

[dominique-pfister]

Currently, the sitemap is returned from a static file sitemap.xml in the document root, which again ESincludes dynamically generated url sets. If indexing isn't configuring in that project (i.e. no `helix-query.yaml present), an empty list is returned. This is bad, since it e.g. makes Google believe that the site is empty. If a 404 is returned instead, Google will crawl the site manually.

Idea: in robots.txt, use the property Sitemap and point it to /cgi-bin/sitemap.js instead.
Or: in our fastly configuration, redirect /sitemap.xml to /cgi-bin/sitemap.js

[rofe]

This is bad, since it e.g. makes Google believe that the site is empty

Maybe it's also desired?

In any case, I like the Fastly redirect better so we can stick with the standard file name.