Add support for various new fields in the Sleep data

[yatharthranjan]

We currently only process a subset of sleep data provided by fitbit. In particular some calculated data are missing such as minsToFallAsleep, timeInBed and more.

[afolarin]

Some useful stuff there indeed... if only there were some way to keep an eye for changes on the Fitbit API 🤔 maybe there's a channel on the forum I need to follow?