Samples aren't listed in Microsoft Docs - Code Samples

None of the samples in this repo are listed in the [Microsoft Docs - Code Samples Browser](https://docs.microsoft.com/en-us/samples/browse/?expanded=dotnet&products=ef-core). From reading their onboarding docs, we need a README.md per sample with YAML front-matter, e.g. https://github.com/dotnet/AspNetCore.Docs/blob/main/aspnetcore/tutorials/grpc/readme.md

I'm happy to help trial onboarding one if we can pick a top sample and get minimum viable metadata to get it submitted. Once that goes through successfully, I propose picking the top 5-10 samples and getting them listed.

+ @roji @JeremyLikness