replace/complement ,-separated listing with standard nargs="+" handling

[yarikoptic]

ATM, e.g. for query (but also others)

Options:
  -nl, --nidm_file_list TEXT      A comma separated list of NIDM files with
                                  full path  [required]
  -nc, --cde_file_list TEXT       A comma separated list of NIDM CDE files
                                  with full path. Can also be set in the
                                  CDE_DIR environment variable

which is VERY inconvenient to operate from shell since I cannot rely on globbing etc, and need to come up with workarounds like @seanhatton did in notes and I implemented in https://github.com/ReproNim/OpenNeuroDerivatives-NIDM/blob/master/code/do-segstats2nidm-perds#L32

pynidm concat -nl "$(echo $(ls -1 sub-*/*"$ttl"_nidm.ttl) | tr " " "," )" -o "$ttl"_nidm.ttl

I think it would have been much better as

pynidm concat -o "$ttl"_nidm.ttl -nl sub-*/*"$ttl"_nidm.ttl

-- could be added, where needed, to separate out end of options from positional args - python argparse already does that by default IIRC.