misc/soliscloud-inverter-control#7: Get expected status endpoint

The soliscloud control API doesn't expose an actual status, so it's not possible to call it and say "is discharging" or "is charging" - those details will come in via the telegraf plugin which talks to the normal API.

What we can do, though, is fetch the config and then process it in order to identify whether we think we're in a scheduled charge/discharge period.

This should probably check all 3 slots, but return a special status if we're charging/discharging from a different timeslot than the one the server uses

Eventually, I'd like this to be used by a healthcheck automation - one that checks HomeAssistant's view against the inverter's reported config. That should help provide a safety net against the fact that we've moved the charge scheduling to a model which requires always on config to work