Levit conversion file argparser bug
### Who can help?

@NielsRogge

### Reproduction

In the conversion file for the `levit` model (`convert_levit_timm_to_pytorch.py`) there is a wrong usage of `argparse.ArgumentParser()` for the `--push_to_hub` argument. Currently it is handled with the type `bool` but in the argparser `bool` type does not work as expected and the current code always generates `push_to_hub=True` not matter if in the CLI we use `--push_to_hub=False` or `--push_to_hub=True`. More canonical convention of handling boolean values with the argparser is to use two arguments. As an example: `--no-push_to_hub` to store `False` values and `--push_to_hub` to store `True` values.


### Expected behavior

Correct usage of the `argparser`.
Closing since fix was merged.