Add JsonProperty-style mapping for case class conversions

E.g. something like:

case class AnalyticsDataset(@JsonProperty("DatasetName") name: String)

• so the underlying JSON field is named DatasetName, but it's copied into the name field in the case class.

A 3rd-party library (the Scala extensions for Jsoniter) is currently used for case class encoding.  It doesn't seem to support this out of the box, so may have to look at alternatives (most likely upickle or Jackson).