Add delayed CLI Definition

[geyang]

This is different from delated parsing (?)

Suppose we have a complex set of configurations, such as the one from legged-gym. We want to include them for argument parsing selectively at runtime.

class Args_1(ParamsProto, cli_parse=False):
      seed = 10

class Args_2(ParamsProto, cli_parse=False):
      prefix = "hey"
      
      
 if __name__ == "__main__":
      Args_1.parse()

And this should only include Args_1 in the argparse list.