.NET 7: Add sample for Minimal API IFormFile and IFormFileCollection Support

[Rick-Anderson]

See https://devblogs.microsoft.com/dotnet/asp-net-core-updates-in-net-7-preview-1/
Sample code goes in https://github.com/dotnet/AspNetCore.Docs/tree/main/aspnetcore/fundamentals/minimal-apis/iformFile/7.0-samples

@JuergenGutsch are you interested in writing a minimal sample?

[Rick-Anderson]

@martincostello this is all yours.

[JuergenGutsch]

I saw it too late :-(
Just in case, I would have samples ready.

[martincostello]

@JuergenGutsch Feel free to work on this instead if you've already got something.

[JuergenGutsch]

Thanks @martincostello
@Rick-Anderson do you agree?

[Rick-Anderson]

@martincostello thanks for being so generous. Hopefully you can find an interesting issue to work on is:issue is:open label:"code help wanted"

@JuergenGutsch thanks for taking this.

[Rick-Anderson]

@JuergenGutsch can you PR some of your samples in https://github.com/dotnet/AspNetCore.Docs/tree/main/aspnetcore/fundamentals/minimal-apis/iformFile/7.0-samples