Send dynamic powerconstraint in flex-model

[ArdJonker]

Use case:
When a V2G user has set a calendar item that during this event no charging or discharging takes place and the schedule is optimised with this constraint.

Suggested format for flex-model:
"consumption-capacity": [
{
"value": 0,
"start": target_start.isoformat(),
"end": target_end.isoformat(),
}
],
"production-capacity": [
{
"value": 0,
"start": target_start.isoformat(),
"end": target_end.isoformat(),
}
],

Related to:
V2G-liberty/addon-v2g-liberty#41

[Flix6x]

Just to note that this requires us to merge two flex model field schemas: SensorOrQuantity and TimeSeriesOrSensor, which streamlines our API syntax and has clear user value.

[Flix6x]

I'm starting to keep track of the functionality of being able to pass a time series directly in the flex-model here: #1134

[ArdJonker]

Great! Eager to try it out on V2G Liberty! Hopefully I can pickup V2G Liberty issue V2G-liberty/addon-v2g-liberty#41 soon.