Add an 'Examples' page to the docs with fully functioning example applications

Nadie ha tomado este issue todavía.

There are a few cases of interesting usages that come up in issues, but which don't seem appropriate to put into our main docs (b/c we don't want to bloat our docs). If we had an Examples page in the docs, we could show off all of our cool ideas for how you can solve problems with `webargs`, but without disrupting the flow of the main documentation.

Specific cases which would be good candidates for example apps:
- [Django App with CSRF-Removing Parser](https://github.com/marshmallow-code/webargs/issues/640#issuecomment-930276628)
- [Axios Query-String Parser](https://github.com/marshmallow-code/webargs/issues/517#issuecomment-634061481)
- Setting a parser to use `unknown=RAISE` on query params

I did a quick scan of closed issues until I hit the 5.x/6.0 transition point, then called it a day. Maybe there are other interesting examples in older issues? Or maybe we have things in other parts of the docs like the upgrade guide which would be nice to separate out (or even just duplicate).

Comienza revisando los comentarios del issue enlazado sobre el Django CSRF-removing parser y el Axios query-string parser; después, inspecciona la documentación existente de webargs y la guía de actualización en busca de otros candidatos. Define la estructura de la Examples page y selecciona un conjunto específico de aplicaciones completamente funcionales. Se considera terminado cuando la página y los ejemplos ejecutables cubren los casos acordados sin sobrecargar la documentación principal.

Escrito por el modelo de indexación a partir del texto del issue.