Nifti files with non-orthonormal directional cosines should be read and the error changed to a warning.

Hi all,

In this PR - https://github.com/InsightSoftwareConsortium/ITK/pull/1868/files ITK introduced an additional constraint on NiFTI files being read.

This has affected users across a variety of technologies which use ITK such as TorchIO, TotalSegmentator, Nvidia AAIA, HD-BET, nnDetection and even ITK-SNAP (with some files working on < v3.6 but not on v3.8 >)

Given so many users see this as unexpected behaviour could the developers investigate whether the constraint is still a reasonable one?

Note: In this issue this was discussed but the solution solved only one failure case related to small voxel sizes - https://github.com/InsightSoftwareConsortium/ITK/issues/2674 - this issue is still affecting users with larger voxel sizes across a variety of technologies

References:
https://github.com/MIC-DKFZ/nnDetection/issues/24
https://github.com/SimpleITK/SimpleITK/issues/1433
https://github.com/fepegar/torchio/issues/669
https://github.com/wasserth/TotalSegmentator/issues/32