Run multiple systematics in one job
This is a rewrite of the retagging script so that we can run multiple systematics in one job. It should allow us to get away from some workarounds like !658 (merged), and hopefully save some bookkeeping.
There are some rough edges (i.e. it might only work on MC20 for now) but these are probably things that @tdingley and @vhomsak can work with. I had to update the jet systematics code a bit, but I managed to get one track and one jet systematic working
Part of these changes required a bit of restructuring for the output files: rather than saving just tracks
and jets
in the output file, there are now groups for each systematic combination. Hopefully the downstream code can work around this.