ENH: Added cf2grib2 translations

CF 'surface_temperature' ('K') -> Grib2 Skin temperature (0, 0, 17)
CF 'toa_outgoing_longwave_flux' ('W m-2') -> Grib2 Net long-wave radiation flux (0, 5, 5)

surface temperature CF definition:
"sea_surface_temperature Sea surface temperature is usually abbreviated as "SST". It is the temperature of sea water near the surface (including the part under sea-ice, if any), and not the skin temperature, whose standard name is surface_temperature. For the temperature of sea water at a particular depth or layer, a data variable of sea_water_temperature with a vertical coordinate axis should be used."