Add desi_find_file

[akremin]

This creates a simple wrapper around desispec.io.meta.findfile so that it can be called from the command line.

[akremin]

Examples:

> desi_find_file "exposure_table" -n 20240411
/global/cfs/cdirs/desi/spectro/redux/kremin/exposure_tables/202404/exposure_table_20240411.csv

> desi_find_file "processing_table" -n 20240411
/global/cfs/cdirs/desi/spectro/redux/kremin/processing_tables/processing_table_kremin-20240411.csv

> desi_find_file "preproc" -n 20240411 -e 234456 -c b9
/global/cfs/cdirs/desi/spectro/redux/kremin/preproc/20240411/00234456/preproc-b9-00234456.fits.gz

[coveralls]

coverage: 30.161% (+0.001%) from 30.16%
when pulling e95d905 on findfileCLI
into 1f75589 on main.

[sbailey]

Looks good, thanks. The failing doctest is from an issue that has already been fixed in main. OK to merge when tests finish without fixing that in this branch.