More Example Files for Axum

[Zayd-McArdle]

Please can we have a lot more example use cases for Axum other than the ones provided in the repo, like uploading and downloading files on the web server, deleting uploaded files, more middleware use cases like json validation, multi-form validation, etc.

I am coming from a C# ASP.NET Core background where a lot of the middleware stuff is abstracted away and we need something for those transitions to this library.

[jplatte]

Check out the Project Showcase in ECOSYSTEM.md :)