chore: add GitHub Packages NuGet source for TizenFX ref packs

Author: Jay Cho

workload/NuGet.config

@@ -9,6 +9,14 @@
     <add key="dotnet6" value="https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet6/nuget/v3/index.json" />
     <add key="dotnet7" value="https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet7/nuget/v3/index.json" />
     <add key="nuget.org" value="https://api.nuget.org/v3/index.json" protocolVersion="3" />
+    <add key="github" value="https://nuget.pkg.github.com/Samsung/index.json" />
   </packageSources>
+  <!--Credential for github is required to reference TizenFX-->
+  <!-- <packageSourceCredentials>
+    <github>
+      <add key="Username" value="" />
+      <add key="ClearTextPassword" value="" />
+    </github>
+  </packageSourceCredentials> -->
   <disabledPackageSources />
 </configuration>