args error when running pl_examples semantic_segmentation through command line
🐛 Bug
Running python pl_examples\domain_templates\semantic_segmentation.py leads to argument options conflicting error.
The issue is the same as the one with #5382
This error seems to be because add_help=True in argparse.ArgumentParser  in both the parent_parser and in the parser for adding model specific args. Setting it to False in only one of either parser seems to fix this and help options work too
To Reproduce
https://colab.research.google.com/drive/1KgByl810j5ux7vmHoGfOz5MfYG3dIwqd?usp=sharing
Error:
Traceback (most recent call last):
  File "pytorch-lightning/pl_examples/domain_templates/semantic_segmentation.py", line 288, in <module>
    parser = SegModel.add_model_specific_args(parser)
  File "pytorch-lightning/pl_examples/domain_templates/semantic_segmentation.py", line 247, in add_model_specific_args
    parser = ArgumentParser(parents=[parent_parser])
  File "/usr/lib/python3.6/argparse.py", line 1666, in __init__
    self._add_container_actions(parent)
  File "/usr/lib/python3.6/argparse.py", line 1435, in _add_container_actions
    group_map.get(action, self)._add_action(action)
  File "/usr/lib/python3.6/argparse.py", line 1565, in _add_action
    action = super(_ArgumentGroup, self)._add_action(action)
  File "/usr/lib/python3.6/argparse.py", line 1375, in _add_action
    self._check_conflict(action)
  File "/usr/lib/python3.6/argparse.py", line 1514, in _check_conflict
    conflict_handler(action, confl_optionals)
  File "/usr/lib/python3.6/argparse.py", line 1523, in _handle_conflict_error
    raise ArgumentError(action, message % conflict_string)
argparse.ArgumentError: argument -h/--help: conflicting option strings: -h, --help

Environment
Google Colab