Start date for ensemble spinup

[SorooshMani-NOAA]

Right now the ensemble spinup starts at the beginning of storm track data. This would require much more resources to run the full course. This is also related to having spin up up to the perturbation point #25.

We need to add an option for setup to default to -2 days prior to perturbation point, or input from the user. Or something like that!

[FariborzDaneshvar-NOAA]

@SorooshMani-NOAA just for documenting our g-chat conversation:

Two-days spinup run starts four days before NHC track date/time, and the hotstart simulation starts two days before NHC track date/time.
You might want to shift date/time two days forward, so the hotstart date/time would be aligned with NHC track.
Thanks!