Add smart function to dynamically set `window_length` and `threshold` for `TimeSeriesRegularizer`

The `TimeSeriesRegularizer` currently sets the `window_length` to 5 and `threshold` to 0.8. This was done to support smaller datasets that wouldn't pass an `infer_frequency` check from WW with higher `window_length` and `threshold` values.

To address this issue, I would suggest including a smart function that changes these parameters based on the size of the dataset (if the user doesn't pass in their own values). Smaller datasets should have more forgiving values (smaller window length and threshold).