Handle soc targets that exceed the maximum planning window

[nhoening]

#569 made a step for state-of-charge targets which lie outside the maximal planning window - they are ignored.

Options for the future:

• Keep disregarding them, but add a warning to the header.
• Raise a validation error in the API
• (Extension of the first option) Make a best guess for the first target that is out of the window, e.g. a linear best-guess so we plan into the right direction.

[Flix6x]

Relevant HTTP header for the first option (but still in draft status): https://datatracker.ietf.org/doc/draft-cedik-http-warning/

[nhoening]

We should actually return these targets in a specific manner in our new API response (where we also mention unreached targets)