Add ecmwf

[dfulu]

Pull Request

Description

Add support for PVNet to use ECMWF NWP data as well as UKV

This replaces the default PVNet model with one which uses the ECMWF data. It leaves the summation model the same though this should be retrained before going into production.

The following environmental variables now need to be set

• NWP_UKV_ZARR_PATH which replaces NWP_ZARR_PATH
• NWP_ECMWF_ZARR_PATH

Checklist:

• My code follows OCF's coding style guidelines
• I have performed a self-review of my own code
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• I have checked my code and corrected any misspellings