[AnVIL DX] Update data modality source

[MillenniumFalconMechanic]

Need

The data modality source is to be updated for the following:

• Datasets: use datasets.data_modality.
• Files: use files.data_modality.

No change required for Activities.

[hunterckx]

The API responses pose two issues for implementing filtering and sorting of data modality:

• datasets.data_modality is not present in termFacets, which prevents dataset data modality from being used as a key for filtering/sorting.
• Beyond that, there's not an appropriate choice of field to reference if we want the data modality filter to be consistent across entity types; there's no data modality field that is both well-populated and available from the APIs for all five entity types -- e.g. datasets.data_modality is only available via the datasets API, while activities.data_modality is available via all APIs but lacks values that are present in datasets.data_modality. Ideally, we would use activities.data_modality, so as to avoid, for example, marking a file as having all data modalities present in the associated dataset.