When analysing MUSE2 output files, sometimes certain input parameters are needed in order to correctly process and interpret the output (e.g. milestone years). As at least some of this data will be needed, we might as well go the whole way and copy the input data to the output folder in its entirety.
As a side benefit, this would also be good for reproducibility, in case the user changes the input files after the fact. We could consider making these copied input files read only.
See: EnergySystemsModellingLab/muse2_data_analysis#5 (comment)