Save forecasts made in the past #210

Verification

• I have searched the existing issues to ensure this feature has not already been requested.

Provide a detailed description of the proposed feature.

Forecasts might only be available past the target_time. I.e a forecast first becomes available at 12:00, for 06:00 that day. Currently we cant save those, as the forcast horizon would be negative (or perhaps its not even) possible

What is the motivation for the feature?

Current in DE

openclimatefix/solar-consumer#258

At around 06:00 the first forecast is available for that day, 00:00 to 23:45.

The forecasts before 06:00 dont change

Outline a potential approach or solution (optional).

Not sure?

Solution might be to save the init_time_utc as 00:00, but then use the created_at_utc for the analysis.