Update setting an extension property

[dkershaw10]

The sample takes a short cut that assumes that the extension property name comes from a property on the application. This won't always be accessible. We should show a different way to "build" the extension property name.

[aloneguid]

      private string FormatExtensionPropertyName(string name)
      {
         return $"extension_{_managementAppClientId.Replace("-", "")}_{name}";
      }