Add nuget.config file to fix NU1507 by only allowing nuget.org as package source. see: https://learn.microsoft.com/en-us/nuget/consume-packages/package-source-mapping and https://github.com/dotnet/sdk/issues/25379 (#10396)

nuget.config

@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="utf-8"?>
+<configuration>
+  <packageSources>
+    <!--To inherit the global NuGet package sources remove the <clear/> line below -->
+    <clear />
+    <add key="nuget" value="https://api.nuget.org/v3/index.json" />
+  </packageSources>
+</configuration>