[Infrastructure] Add blazor feed

Author: javiercn

NuGet.config

@@ -21,5 +21,6 @@
     <add key="aspnetcore-dev" value="https://dotnet.myget.org/F/aspnetcore-dev/api/v3/index.json" />
     <add key="aspnetcore-tools" value="https://dotnet.myget.org/F/aspnetcore-tools/api/v3/index.json" />
     <add key="roslyn-tools" value="https://dotnet.myget.org/F/roslyn-tools/api/v3/index.json" />
+    <add key="blazor-wasm" value="https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet3.1-blazor/nuget/v3/index.json" />
   </packageSources>
 </configuration>