.NET Framework on Windows image

This Dockerfile builds a Windows image (the big one, not Windows Server Core) with .NET Framework 4.8.

The Dockerfile is based on https://github.com/microsoft/dotnet-framework-docker/blob/master/4.8/runtime/windowsservercore-ltsc2019/Dockerfile with a few changes

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< FROM mcr.microsoft.com/windows/servercore:ltsc2019
---
> FROM mcr.microsoft.com/windows:1809
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> USER ContainerAdministrator

The main difference is that the big Windows image has the default user ContainerUser instead of ContainerAdministrator and therefore does not have enough permission to install software.