adding readonly input fields to the input_spec

[djarecka]

• allowing to add a completely new input fields as a part of inputs_metadata. This can be useful when complicated xor structure is required by the tool. Example would be fslroi that has three different option:

fslroi <input> <output> <xmin> <xsize> <ymin> <ysize> <zmin> <zsize>
fslroi <input> <output> <tmin> <tsize>
fslroi <input> <output> <xmin> <xsize> <ymin> <ysize> <zmin> <zsize> <tmin> <tsize>

Nipype has some xor structure that doesn't fully cover all usecases, see here.

In pydra we could probably handle this by adding readonly arguments like this:

  inputs_metadata:
    x-z_range:
      readonly: True
      argstr: "{x_min} {x_size} {y_min} {y_size} {z_min} {z_size}"
      requires: [x_min, x_size, y_min, y_size, z_min, z_size]
      position: 2

    t_range:
      readonly: True
      argstr: "{t_min} {t_size}"
      requires: [t_min, t_size]
      position: 3