Update Dockerfiles to use mcr.microsoft.com

[rkttu]

Recently, while looking at the sample code, there was a problem that the Dockerfile could not receive some base images. Upon investigation, it seemed that the Dockerfile needed to be modified.

• microsoft/dotnet:2.2-sdk-nanoserver-1809 -> mcr.microsoft.com/dotnet/core/sdk:2.2-nanoserver-1809
• microsoft/dotnet:2.2-runtime-nanoserver-1809 -> mcr.microsoft.com/dotnet/core/runtime:2.2-nanoserver-1809
• microsoft/dotnet:2.2-aspnetcore-runtime-nanoserver-1809 -> mcr.microsoft.com/dotnet/core/aspnet:2.2-nanoserver-1809
• microsoft/dotnet:2.1-aspnetcore-runtime-nanoserver-1809 -> mcr.microsoft.com/dotnet/core/aspnet:2.1-nanoserver-1809
• microsoft/dotnet:2.1-sdk-nanoserver-1809 -> mcr.microsoft.com/dotnet/core/sdk:2.1-nanoserver-1809
• microsoft/dotnet:2.1-runtime-nanoserver-1809 -> mcr.microsoft.com/dotnet/core/runtime:2.1-nanoserver-1809
• microsoft/dotnet-framework:4.7.2-sdk-windowsservercore-ltsc2019 -> mcr.microsoft.com/dotnet/framework/sdk:4.7.2-windowsservercore-ltsc2019