Add binary classification task IDs
As a precursor to aligning the task IDs in `datasets` and AutoTrain, we need a way to distinguish binary vs multiclass vs multilabel classification.

This PR adds binary classification to the task IDs to enable this.

Related AutoTrain issue: https://github.com/huggingface/autonlp-backend/issues/597

cc @abhishekkrthakur @SBrandeis 