The exposes entry looks similar to a switch, except the type is a
"light" and it has `state` and `brightness`. Tested only on single
channel dimmers.
Also added a PercentageTranslator to translate between the HomeKit
`brightness`, which is a percentage, to/from an arbitrary numeric value
in Z2M.
encoding/json would refuse to implicitly cast the numbers into strings.
Currently we don't use these values, so let's preserve their type using
`any` for now.
An example is `keep_time` for occupancy sensors, where it's
[30, 60, 120] seconds.
