open-ifs format

The idea is to make HERMESv3_GR able to write grib2 format in the Open-IFS grid (Reduced gaussian grid)

After some exploration ad meeting with @mariag we decided to follow this:

1. Play in regular lat-lon grid as HERMES current does.
2. Transform it to a regular lat-lon grib2 file with EcCodes
3. Re-grid it to the regular gaussian grid with MetView

• We need that regular lat-lon grib2 intermediate file