Forecast: add energy demand metrics (experimental)

[andig]

Start collecting energy metrics. Next step: better algorithms taking these metrics into account, for example peak shaving (#18934). This PR adds the following features:

• track daily PV generation (energyDemand.solarActual- generated until now)
• calculate forecasted generation (energyDemand.solarForecasted- until now)
• calculate an adjusted solar forecast based on actual generated vs. forecasted energy (forecast.solarAdjusted)
• calculate potential energy demand for battery and vehicles (energyDemand.batteryDemand and energyDemand.loadpointDemand)

@naltatis ein erster Schritt damit auch aktiv etwas anzustellen. Würdest Du die im UI ergänzen wollen?

TODO

• use actual planner targets instead of theoretical vehicle limit in plan exists
• add a household base load and household demand
• calculate peak shaving demand