Refactoring NWP readers

[ecasellas]

Currently, each NWP has a specific reader function; however, most of the functions share some similarities and may be refactored. Unimodel has twelve model readers, and some of them can be merged into different new functions:

read_nwp_grib

Apart from reading the grib, it includes the functionality of renaming longitude/latitude to x/y. This function should include the following models: ICON, ECMWF, UM, NCEP, WW3, SWAN.

_get_nwp_metadata

Retrieves projection CRS from xarray data. It can be used for the following models: ICON, ECMWF, UM, NCEP, WW3, SWAN, Meteofrance, WRF-TL-ENS.

get_meteofrance_grib

Apart from what is included in read_nwp_grib, it should also include rounding coordinate x/y values round(2) for AROME and round(1) for ARPEGE. Merge of read_arome_grib and read_arpege_grib.

get_cnr_isac_grib

Apart from what is included in read_nwp_grib, it should also include the creation of x and y coordinates from geotransform and dropping longitude and latitude coordinates. Function to read MOLOCH and BOLAM model gribs.

_get_cnr_isac_metadata

Merge of _get_bolam_metadata and _get_moloch_metadata.

get_wrf_tl_ens_grib

Leave as is, but change specific metadata by _get_nwp_metadata.

unimodel.io.interface must be changed accordingly.