making the running of epi plotting dependant on whether config had been provided. Modifying tests to stop using epi outputs which are no longer included

adding ability to set additional values to the run config from the command line args (if not already present in the config json)
modifying the epi processor to look for CalculationSpanDays in both the config json and the command line args, as preparation for use with the Epi fitting, which will pass calcspan as an arg

Also fixes 'issue date' in plots.

Merge branch 'main' of gitlab.developers.cam.ac.uk:gilligan-epid/wheat-rusts/ews-coordinator into main

removing the need for a spatial points file in met_extractor assets to check the output dimensions, now compared to the input nc that created the results