Add Forecast.Solar solar forecast

[andig]

@naltatis as simplified alternative to #9454 and without integrating the forecast into planning, it might be nice to displace a solar forecast (in W). Short-term it would be nice to collect and log the data for forecast/actual comparison, later use it for forecasting.

Is this something you'd be interested in including?

From                   To                     Price/Cost
2025-01-18 10:19:34    2025-01-18 10:19:34    0.000
2025-01-18 11:00:00    2025-01-18 11:00:00    678.000
2025-01-18 12:00:00    2025-01-18 12:00:00    1108.000
2025-01-18 13:00:00    2025-01-18 13:00:00    1390.000
2025-01-18 14:00:00    2025-01-18 14:00:00    1508.000
2025-01-18 15:00:00    2025-01-18 15:00:00    1578.000
2025-01-18 16:00:00    2025-01-18 16:00:00    1851.000
2025-01-18 17:00:00    2025-01-18 17:00:00    1861.000
2025-01-18 18:00:00    2025-01-18 18:00:00    1227.000
2025-01-18 18:42:40    2025-01-18 18:42:40    0.000
2025-01-19 10:18:30    2025-01-19 10:18:30    0.000
2025-01-19 11:00:00    2025-01-19 11:00:00    1377.000
2025-01-19 12:00:00    2025-01-19 12:00:00    2200.000
2025-01-19 13:00:00    2025-01-19 13:00:00    2767.000
2025-01-19 14:00:00    2025-01-19 14:00:00    3055.000
2025-01-19 15:00:00    2025-01-19 15:00:00    2995.000
2025-01-19 16:00:00    2025-01-19 16:00:00    2679.000
2025-01-19 17:00:00    2025-01-19 17:00:00    2025.000
2025-01-19 18:00:00    2025-01-19 18:00:00    1279.000
2025-01-19 18:44:21    2025-01-19 18:44:21    0.000

TODO

• solar tariff type @andig
• ui @naltatis
• solar docs group @naltatis

[naltatis]

Good idea to start with a display only integration. Makes things a lot easier.
I'll think about how to visualize/integrate this data in a first iteration. A simple "expected kWh of solar energy in the next 24h" information in the main UI could be a good entry point.