Web APIs must set a non-HTML content-type on all responses, including 300s, 400s and 500s #23

This recommendation comes from #18.

We should enforce this at the root level: if the result is a HTML-like content-type, we should force it to something else. This should be possible with a simple middleware.
Maybe that exists in a ready-to-use package already.

┆Issue is synchronized with this Jira Task