Recipe: building an instrumentation plugin for Falcon

Write a documentation article or recipe on how one could build a new monitoring / metrics collection / "instrumentation" plugin for Falcon.

Discuss different approaches:
* Providing middleware that users can add to a Falcon app
* A plugin that monkey-patches `falcon.App`
* A plugin that wraps the whole application, acting [generic WSGI middleware](https://www.python.org/dev/peps/pep-3333/#middleware-components-that-play-both-sides)

Some ideas: https://gist.github.com/vytas7/e0197eff2e87705a3df33d63123f3d26

See also:
* https://github.com/falconry/falcon/issues/1828
* https://github.com/falconry/falcon/issues/10