Support hiding entry points with `x-hidden`
Support hiding entry points with `x-hidden`

This patch adds a small, private extension that lets us hide private entry
points from the docs by adding an `x-hidden` boolean property at the method
level. This is occasionally useful for "boilerplate" entry points like /robots.txt.

There are discussions about more advanced ACL-based doc hiding at
https://github.com/OAI/OpenAPI-Specification/issues/433, but those haven't
lead anywhere yet. This is a simple solution that will work in the meantime.

wikimedia/hyperswitch