TimeAsFeature transform

[sdaulton]

Summary: This implements a transform for adding start_time and duration as features for modeling. Currently, this adds them as RangeParameters (to unblock time-sensitive applications), but in the future it would be good to revise this with a better treatment of non-tunable contextual information.

duration appears to lead to better model fits on the synthetic example (notebook) than using end_time. This also works better than using the midpoint between start time and end time.

Reviewed By: bernardbeckerman, Balandat

Differential Revision: D57082939