IRIDL server-side processing

Server-side processing:
- [x] select and aggregate `lead_time` `L` and `forecast_time` `S`
- [x] regrid `X` and `Y` to 1.5 deg grid
- [x] SubX intake catalog biweekly 
- [x] requires unreleased climetlab_s2s_ai_challenge plugin
- [ ] init frequency forecast: keep as todo
- [x] IRIDL cat S2S 
- [x] IRIDL obs regrid
- [x] check proper lead ints or floats to match my int lead_time

closes #9

See merge request aaron.spring/s2s-ai-challenge-template!10