Mrtrix3's DWIPreproc force inputs that are not mandatory

[GalKepler]

Summary

The interface to Mrtrix3's dwifslpreproc forces some inputs that are not really necessary according to the original CLI on which it relies.

Actual behavior

The interface requires inputs to be set for out_grad_mrtrix, pe_dir, etc.

Expected behavior

Ideally, it would change the necessary inputs (that are different and depends on the way you use this CLI).
A simpler solution would be to simply reduce the mandatory inputs to those that truly are.

python -c "import nipype; from pprint import pprint; pprint(nipype.get_info())"
-->

{'commit_hash': 'd77fc3c',
 'commit_source': 'installation',
 'networkx_version': '2.6.3',
 'nibabel_version': '3.2.1',
 'nipype_version': '1.8.0',
 'numpy_version': '1.20.0',
 'pkg_path': '/home/groot/Projects/PhD/venv/lib/python3.9/site-packages/nipype',
 'scipy_version': '1.7.3',
 'sys_executable': '/home/groot/Projects/PhD/venv/bin/python',
 'sys_platform': 'linux',
 'sys_version': '3.9.12 (main, Mar 24 2022, 16:20:11) \n[GCC 9.4.0]',
 'traits_version': '6.3.2'}

Execution environment

• My python environment outside container