Pass halo indices from a file

[robjmcgibbon]

Adds a --halo-indices-file argument to compute_halo_properties, so that large numbers of halo indices can be passed in a text file. tests/COLIBRE/run_L0025N0188_Thermal.sh now uses the new flag with tests/COLIBRE/halo_indices_0092.txt

SOAP/core/combine_args.py gains COMMAND_LINE_ONLY_PARAMETERS, a deny-list which makes SOAP exit with an error if any of those arguments appear in the Parameters section of the config file.

In SOAP/core/halo_centres.py rank 0 reports how many of the requested indices were matched and writes any unmatched ones to <catalogue_name>_unmatched_halo_indices.txt in the working directory.

flush=True added to every print immediately preceding a comm.Abort across SOAP/, misc/ and tests/ (stops messages being lost when MPI killed the process)

README gains a command line argument reference plus a halo-selection section