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

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
• Axios Query-String Parser
• 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).

まず、Django CSRF-removing parser と Axios query-string parser に関するリンク先の issue のコメントを確認し、次に既存の webargs ドキュメントと upgrade guide を調べて他の候補を探します。Examples page の構成を定義し、完全に動作するアプリケーションを絞り込んで選定します。ページと実行可能な例が合意したケースを網羅し、メインドキュメントを肥大化させていなければ完了です。