text: Title: FAQ item on RequestOptions.keep_blank_qs_values is outdated/incorrect
  Body: At the time of writing, the FAQ item ["Why is my query parameter missing from the req object?"](https://falcon.readthedocs.io/en/stable/user/faq.html#why-is-my-query-parameter-missing-from-the-req-object) states that
  > If a query param does not have a value, Falcon will by default ignore that parameter. For example, passing `'foo'` or `'foo='` will result in the parameter being ignored.
  
  As of Falcon 2.0+, this is incorrect, and the default value for [`RequestOptions.keep_blank_qs_values`](https://falcon.readthedocs.io/en/stable/api/app.html#falcon.RequestOptions.keep_blank_qs_values) is `True`.
  
  However, I believe we should still keep the FAQ item in the case one has set the option to `False` for any reason (or maybe someone else working on the same code base has done that), and is wondering what's going on.