add rrdesi --model option to desi_zproc

[sbailey]

This PR adds the rrdesi --model ... option to the desi_zproc workflow so that redrock models are automatically output as part of the pipeline.

Example job script /global/cfs/cdirs/desi/users/sjbailey/spectro/redux/rrmodel/run/scripts/tiles/cumulative/11607/20240408/ztile-11607-thru20240408.slurm ran

srun -N 1 -n 64 -c 2 --gpu-bind=map_gpu:3,2,1,0 --cpu-bind=cores desi_zproc -t 11607 -g cumulative -n 20240408 -e 235004 -c a0123456789 --mpi --run-zmtl --max-gpuprocs 4

which ran rrdesi commands like

redrock.external.desi.rrdesi([
'-i', '/global/cfs/cdirs/desi/users/sjbailey/spectro/redux/rrmodel/tiles/cumulative/11607/20240408/coadd-0-11607-thru20240408.fits',
'-o', '/global/cfs/cdirs/desi/users/sjbailey/spectro/redux/rrmodel/tiles/cumulative/11607/20240408/redrock-0-11607-thru20240408.fits',
'-d', '/global/cfs/cdirs/desi/users/sjbailey/spectro/redux/rrmodel/tiles/cumulative/11607/20240408/rrdetails-0-11607-thru20240408.h5',
'--model', '/global/cfs/cdirs/desi/users/sjbailey/spectro/redux/rrmodel/tiles/cumulative/11607/20240408/rrmodel-0-11607-thru20240408.fits',
'--gpu', '--max-gpuprocs', '4'])

with output in /global/cfs/cdirs/desi/users/sjbailey/spectro/redux/rrmodel/tiles/cumulative/11607/20240408 including rrmodel*.fits files.

This is a followup to desihub/redrock#283 which added the rrdesi --model option.

[akremin]

Thanks the changes are minimal and does what we want. When checking the log I did identify a minor redrock issue (desihub/redrock#301) but that is unrelated to this PR. I will approve and merge this.