Support setting Charge on Solar

Now that we have Charge On Solar available, it would be nice to have Controls for "Charge on Solar" on / off, setting the solar charge level apart from the already-available top charge level.

This would allow, for example, using Schedules for starting a "grid charge" in the evening if "charge on solar" never reached the desired state of charge for the morning commute. This feature is missing from Charge On Solar but can easily be done via TeslaFi Schedules + Controls, if these extra controls are added.