Add support for multi-label classification datasets like alkzar90/NIH-Chest-X-ray-dataset from Hugging Face

[eloy-encord]

When adding the JSON definition of the alkzar90/NIH-Chest-X-ray-dataset Hugging Face medical dataset, found that it's a multi-label dataset instead of a multiclass.

JSON definition:

{
  "dataset_type": "HFDataset",
  "title": "NIH-Chest-X-ray",
  "title_in_source": "alkzar90/NIH-Chest-X-ray-dataset",
  "name": "image-classification",
  "target_feature": "labels",
  "trust_remote_code": true
}

Would be great to consider adding support for multi-label datasets, where this dataset may serve as the starting test dataset.