pass through cmd-line arguments to configure datamodel_code_generator

[svilendobrev]

g'day

as this is using datamodel_code_generator which is very configurable, would be very useful if arguments for it can be passed through (maybe as subparser https://docs.python.org/3/library/argparse.html#sub-commands)

maybe also reuse whatever file structure that datamodel_code produces, instead of inventing a new one..