Use static data as additional data input for kienzler

[the-infinity]

With ParkenDD/parkapi-static-data#6 , there will be a geojson which should be used as mixin for Kienzler boxes at the static data handling. Please extend the static Kienzler base converter with the ability to get these GeoJSONs, and mix the properties into the properties from Kienzlers API.

If the GeoJSON should be fetched and mixed in at all should be controlled by a property of the base class, which should be false by default, and can be activated in the subclasses.

Please re-use the existing GeoJSON validators when implementing this feature.

Please use https://raw.githubusercontent.com/ParkenDD/parkapi-static-data/refs/heads/main/sources/{source.uid}.json as GeoJSON URL.

If a dataset exists in Kienzler API, but not in the GeoJSON, that's fine, please add the dataset anyway, just without the extended data from the GeoJSON. If it's the other way around, dataset in GeoJSON, but not in Kienzler, please ignore this dataset.