Passing arguments as config data class

[ajmedford]

I think it would be very helpful if the config passed to AtomsTrainer used in many of the examples could be wrapped into a class (perhaps a dataclass). The structure of the class is basically already provided in https://amptorch.readthedocs.io/en/latest/usage.html but it is currently very easy to make a mistake or get lost amongst default values. This should also aid development going forwards.

[ajmedford]

@jparas-3 is currently working on this in another fork and will merge the changes once they are completed: https://github.com/jparas-3/amptorch/tree/config_dataclass