wcst_import - supports to import one variable from GRIB file with multiple variables

[Bang Pham Huu]

Normally, GRIB file contains only one variable, however, ECMWF ERA5 GRIB has 4 bands in one file and wcst_import cannot import that.

In this case, one can select one variable in the GRIB recipe, e.g.

"slicer": {
	"type": "grib",
	"pixelIsPoint": true,
	"bands": [{
		"name": "2m_dewpoint_temperature",
		"identifier": "2d"
	}],

and wcst_import should filter from the GRIB file which messages having msgId for this band (2d).