Add loadpoint config api (BC)

[andig]

Fix https://github.com/evcc-io/evcc/issues/12903

This PR deprecates the following yaml loadpoint settings:

• mode
• title
• phases
• min/max current
• priority

TODO

• [x] UI for loadpoint properties @naltatis
• [ ] UI for adding/changing charger @naltatis
• [x] UI for adding/changing lp meter @naltatis
• [ ] e2e tests @naltatis
• [x] UI default vehicle select @naltatis
• [ ] UI circuit assignment @naltatis
• [ ] API for assignable circuits @andig
• [ ] API set meter, charger, defaultVehicle @andig
• [x] UI for adding/removing loadpoints @naltatis
• [ ] API for adding/remove loadpoints @andig
• [x] implement config as settings
• [x] unable to save priority=0 @andig
• [ ] decide/adapt migration strategy (use evcc migrate?) @andig @naltatis
• [ ] remove orphan meters/chargers (no site/loadpoint ref) on startup