make _add_dataclass_options public

[martinResearch]

Hi,

I would like to be able to use _add_dataclass_options directly in some of my code in order to be able to continue using normal argparse.ArgumentParser instances and use a dataclass to define only a subset of my script arguments.
Would it be possible to expose _add_dataclass_options as a public function i.e. remove the initial underscore?

[mivade]

I don't see why not. Feel free to make a pull request!