Support for mutually exclusive groups

[fennerm]

Describe the solution you'd like
It would be nice if argparse's mutually exclusive argument groups could be supported. If arguments are placed in a mutually exclusive group, the help message should indicate them by listing as --option_a | --option_b | .... Argdantic should verify that at least one of the arguments in the group was passed.

Describe alternatives you've considered
Currently we can handle by adding extra verification in the main func, but the help message is not so clear

[edornd]

Hi @fennerm, this is already done by booleans, but it sounds indeed as something that could be more "general purpose". In short, it is definitely feasible, I just don't have a clear (and clean) idea on how to define a group in practice, when defining the arguments 🤔 pydantic itself has no built-in way to define them, [either than provide a validator ].(pydantic/pydantic#522 (comment))