Assign package source mappings

Author: jimmylewis

nuget.config

@@ -6,4 +6,18 @@
     <add key="dotnet-myget-legacy" value="https://pkgs.dev.azure.com/dnceng/public/_packaging/myget-legacy/nuget/v3/index.json" />
     <add key="vs" value="https://pkgs.dev.azure.com/azure-public/vside/_packaging/msft_consumption/nuget/v3/index.json" />
   </packageSources>
+
+  <packageSourceMapping>
+    <packageSource key="dotnet-public">
+      <package pattern="*" />
+    </packageSource>
+    <packageSource key="dotnet-myget-legacy">
+      <package pattern="Microsoft.Extensions.CommandLineUtils.Sources" />
+    </packageSource>
+    <packageSource key="vs">
+      <package pattern="Microsoft.Test.Apex.VisualStudio" />
+      <package pattern="Microsoft.VisualStudio.Internal.MicroBuild" />
+      <package pattern="Microsoft.WebTools.Languages.*" />
+    </packageSource>
+  </packageSourceMapping>
 </configuration>