optional Output of label probability maps by nnUnet

### A short summary of what you would like to see in BIBSnet.

I was wondering if an additional output could be generated if requested, which would be the voxel-wise probabilities of each label. I think that you can get the raw probability maps by enabling the softmax export: e.g.
nnUNet_predict \
-i INPUT_FOLDER \
-o OUTPUT_FOLDER \
-t TASK_ID \
-m 3d_fullres \
--save_npz

This might be useful to some folk who might want to differentiate between different WM probabilities, for example.

### Do you have any interest in helping implement the feature?

Yes, but I would need guidance

### Add any additional information or context about the request here.

_No response_