Add variables to ECMWF IFS ENS

[aldenks]

10fg (10m wind gust)

tcc (total cloud cover)

t_925 (temperature at 925 hPa)

t_850 (temperature at 850 hPa)

gh_925 (geopotential height at 925 hPa)

gh_850 (geopotential height at 850 hPa)

• PR Add gust, cloud cover, and 925 and 850hPa temp and gh to ECMWF IFS ensemble forecast #485
• backfill
• run validation
• update notebook
• update docs

[aldenks]

Done! https://dynamical.org/catalog/ecmwf-ifs-ens-forecast-15-day-0-25-degree/