Write script to convert ESO PV forecasts to NetCDF

[JackKelly]

Detailed Description

The ESO PV forecasts are provided as a set of CSV files.

Convert these to a single NetCDF file.

• Split the ASL and ML forecasts into two separate xr.DataArrays
• Only take the 2 day forecasts

This is a sub-task of #35

Possible Implementation

Python script

[JackKelly]

The script in PR #37 runs and appears to create a valid NetCDF file of all the ESO PV forecasts :)