Compute first unmet targets

[Flix6x]

We'd like the API endpoint for fetching a schedule to return extra information, maybe under the "scheduler_info" key:

• For the first upcoming "soc-minima" value, return the difference between the scheduled SoC at that time and the "soc-minima" value.
• Likewise for "soc-maxima".
• The "soc-targets" can be left out for now, as they are still modelled as hard constraints (so by definition the scheduler won't allow any deviation). This should be documented.
• The scheduling job should do the computation, so we either need to store the computed values in a sensor, or make use of the job results to store the computed values. Related in terms of using job results: Allow retrieving schedules/forecasts from Redis over Postgres #2028