rename experimental modality -> experimental approach?

[tgbugs]

@UlrikeS91 @lzehl @satra for many people modality => data modality, whereas experimental approach is more nebulous (which we want in this case since approach conflates data modality, technique, paradigm, etc.). This would avoid the overlap in terminology, but we will need to update our communities on the preferred terminology (in this case the label of the superclass). Thoughts?

xref https://github.com/HumanBrainProject/openMINDS_controlledTerms/issues/36