sonnenBatterie: implement grid charging

[rivengh]

Fix #15926

This PR adds the grid charging capability to the existing battery control for sonnenBatterie via official sonnenBatterie JSON APIv2.

The power for grid charging can be adapted to the inverter power of the sonnenBatterie via the chargepower configuration parameter (default: 3300W).

This modification has been verified with my sonnenBatterie eco8.

[andig]

Klasse, vielen Dank!

[mabasger]

Vielen Dank!

[tonerbrogan]

Hello,
great work. Many thanks for that.
I have one more question or suggestion:
When the battery recognizes “cheap grid charging”, it always charges up to 100% for me. Would it be possible to implement it so that the battery only charges to the set prioritization value?
(“Prioritize the house battery up to XX%”)
The advantage would be that the battery, depending on the setting, would still have capacity to absorb solar power from the PV and not feed it into the grid when the battery is full.