Modify the way parametric modulation is dealt with

[Remi-Gau]

Currently the way parametric modulations are handled is not very explicit.

See here

You must have some pmod_* column present but it is not explicit to what conditions this modulation is used.

https://github.com/cpp-lln-lab/bidspm/blob/bbab3691daf89bcebc4046974bce339b1abd76d2/demos/face_repetition/models/model-faceRepetitionParametric_smdl.json#L33-45

Better to make things more explicit in the Software section of the bids stats model, so that it can also better align with nipype interfaces:

https://nipype.readthedocs.io/en/latest/api/generated/nipype.algorithms.modelgen.html#specifymodel

Probably something along the lines:

"Software": {
                    "SPM": {
                        "SerialCorrelations": "AR(1)",
                        "Description": "list what conditions we must apply the modulation to and what values are used for the modulation.",
                        "ParametricModulations": [
                            {
                                "Name": "pmod_loss",
                                "Conditions": [
                                    "trials"
                                ],
                                "Values": [
                                    "loss"
                                ]
                            },
                            {
                                "Name": "pmod_gain",
                                "Conditions": [
                                    "trials"
                                ],
                                "Values": [
                                    "gain"
                                ]
                            }
                        ],
                        "PolynomialExpansion": 1
                    }
                }