Passing the power capacity with a sensor ID is not supported

[victorgarcia98]

          @victorgarcia98 I don't think we actually support passing this as a sensor ID. It looks like in `MetaStorageScheduler._prepare` we only support a `Quantity` right now:

flexmeasures/flexmeasures/data/models/planning/storage.py

Lines 114 to 134 in 8b25ae9

	# Check for required Sensor attributes
	power_capacity_in_mw = self.flex_model.get(
	"power_capacity_in_mw",
	self.sensor.get_attribute("capacity_in_mw", None),
	)
	if power_capacity_in_mw is None:
	raise ValueError(
	"Power capacity is not defined in the sensor attributes or the flex-model."
	)
	if isinstance(power_capacity_in_mw, ur.Quantity):
	power_capacity_in_mw = power_capacity_in_mw.magnitude
	if not (
	isinstance(power_capacity_in_mw, float)
	or isinstance(power_capacity_in_mw, int)
	):
	raise ValueError(
	"The only supported types for the power capacity are int and float."
	)

Originally posted by @Flix6x in #897 (comment)

[Flix6x]

Rather than reverting the schema change for the site-power-capacity back to QuantityField, I believe the implementation is straightforward.

In MetaStorageScheduler._prepare the site power capacity is used as a max_value of get_continuous_series_sensor_or_quantity, which uses it to do a .clip(upper=max_value) under the hood. Here, Pandas already supports passing a pd.Series.

So, it should be a matter of simply adjusting some type annotations and fetching the sensor data using get_continuous_series_sensor_or_quantity instead of raising in case the site power capacity is pointing to a sensor.

[victorgarcia98]

Good idea, I'll work on it