text: Title: Why does NHiTS need the target variable specified in the time_varying_unknown_reals attribute?
  Body: I was wondering why do I need to specify the target variable twice, when building a `TimeSeriesDataset` for a **NHiTS**? Once for the attribute 'target' and once for 'time_varying_unknown_reals'. If I don't specify it for the second attribute, I get a `ValueError: [target_name] is not in list.`