Selective integration of consolidation PR #25 - dotnet5 nuget feed (#26)

Author: trylek

NuGet.config

@@ -11,6 +11,7 @@
       one as a template. The following line is a marker to insert the test restore sources.
     -->
     <!-- TEST_RESTORE_SOURCES_INSERTION_LINE -->
+    <add key="dotnet5" value="https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet5-transport/nuget/v3/index.json" />
     <add key="dotnet-core" value="https://dotnetfeed.blob.core.windows.net/dotnet-core/index.json" />
     <add key="dotnet-coreclr" value="https://dotnetfeed.blob.core.windows.net/dotnet-coreclr/index.json" />
     <add key="nuget.org" value="https://api.nuget.org/v3/index.json" />