Make completeness file name configurable in GDE_gather_SERA_and_OBM.py
The name of the CSV file containing completeness data is hard-coded (https://git.gfz-potsdam.de/dynamicexposure/legacy/gde_calculations_prototype/-/blob/master/GDE_gather_SERA_and_OBM.py#L60). Make it a parameter of the configuration file.