Use System.Diagnostics.Activity.AddException in System.ClientModel ActivityExtensions when using .NET 9 +

[m-redding]

AddException - https://learn.microsoft.com/en-us/dotnet/api/system.diagnostics.activity.addexception?view=net-9.0 was added in .NET 9. We should use this method instead of the private method in ActivityExtensions once we can upgrade System.Diagnostics.DiagnosticSource to .NET 10.