Add wrf dwnsca

[tdcwilliams]

Add datasets for WRF forcing.

Needed some changes to datasets:

• convertTargetXY generalised, which assumed GridToMesh interp if interp_latlon=false
  • this worked for other MeshToMesh datasets since they had same central longitude
  • it also assumed the GridToMesh datasets had the same earth shape as nextsim and ASR
• rotation_angle redefined as negative of what it was, since it was just multiplied by -1 when it was used
  • could this affect the coupling
• clarified role of grid.mpp_file in datasets
  • question about coupling datasets: should it be NpsNextsim.mpp or the projection file from the config file. I am asking since it is currently an option to change it - are these specific to central lon = -45 and the usual earth shape, or do you mean to just use what nextsim is currently using?
  • @gboutin-lops, would you mind doing a quick run with this branch to see it doesn't affect the coupled results?

Tested on:

• cs2_smos, osisaf_ice_type (ice_type=cs2_smos)
• icesat, osisaf_ice_drift (ice_type=icesat)
• topaz
• etopo
• era5
• cfsr
• asr

[einola]

Is this ready to be reviewed? If not, can you please convert the PR to a draft (it's a link below the list of reviewers)?