Add FileProvider support

[tladesignz]

This could also be interesting for our app, depending of the direction it should move:

With this, we can be a folder inside the "Files" app:

https://developer.apple.com/documentation/fileprovider

[foundscapes]

@tladesignz is this still relevant?

[tladesignz]

Since Save is very much focused on the whole upload process, it doesn't seem so.

Unless you want Save to become a media management tool, where it's supposed to store media in its app belly potentially forever.

I'd advise against that, though. This would probably mean, that Save would need to get a deeper connection to backends also, where the data is flowing back onto the device, too. That would mean to lose our focus.

[foundscapes]

gotcha, out of scope.