Allow to download many files in a folder

[paule96]

With newer browsers it is possible to access the files system of a user. (with limited access but possibel)
To improve the download experience we should allow a button like download all, that will open a dialog to choose a folder and then the browser can create and download all files to that folder.

That will also allow us to controll how much parallel downloads we want.

More information can be found here:

https://web.dev/file-system-access/#opening-a-directory-and-enumerating-its-contents

[paule96]

https://github.com/KristofferStrube/Blazor.FileSystemAccess

maybe this could help ✌️