Add back Smoke-test package feed

Author: dseefeld

smoke-testNuGet.Config

@@ -22,5 +22,6 @@
     <!--End: Package sources managed by Dependency Flow automation. Do not edit the sources above.-->
     <add key="source-built-packages" value="SOURCE_BUILT_PACKAGES" />
     <add key="dotnet-public" value="https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet-public%40Local/nuget/v3/index.json" />
+    <add key="smoke-test feed" value="SMOKE_TEST_PACKAGE_FEED" />
   </packageSources>
 </configuration>