System.CommandLine incorrect docs about DefaultValueFactory

[piskov]

Describe the issue or suggestion

https://learn.microsoft.com/en-us/dotnet/standard/commandline/get-started-tutorial#add-subcommands-and-custom-validation

If I understand correctly the highlited code is never executed because default value factory is called only when no value provided via CLI call.

The highlighted bit should probably be in the CustomParser as of 2.0