Add nargs='...'  to the reference of add_argument in argparse

# Documentation

The [reference](https://docs.python.org/3/library/argparse.html#nargs) for the `nargs` parameter of `add_argument`  does not include the case when `nargs` is `'...'`. A pull request is provided that adds this case to the documentation, including an example of the use.



### Linked PRs
* gh-101473