In each url of urls.py, if we want to mark an endpoint as being
intentionally undocumented, then in the kwargs instead of directly
mapping like 'METHOD': 'zerver.views.package.foo', we can provide
a tag called 'intentionally_undocumented' and map like:
'METHOD': ('zerver.views.package.foo', {'intentionally_undocumented'}).
If an endpoint is marked as intentionally undocumented, but we find
some OpenAPI documentation for it then we'll throw an error, in which
case either the 'intentionally_undocumented' tag should be removed or
the faulty documentation should be removed.