desi_job_graph makes job dependency and status graph webpage

[sbailey]

This PR adds a script that makes a webpage with the job dependency graph and status for a given night, e.g.

Clicking on a box takes you to the log for that job. This graph is based upon the processing table and SLURM job return codes; it does not check for missing job outputs like the dashboard and if any steps were run outside of the pipeline scripts that update the processing table, this won't know about them. Overall the dashboard is better for getting the big picture across many nights and for checking actual file outputs, while I find this view to be easier to identify what steps went wrong when there is a problem in a night, and for distinguishing "crashed" from "in progress".

Currently this is a single script for simplicity. If we find that we want to call it from other code (e.g. a spin webapp), it could be factored out into a separate module of desispec.

usage: desi_job_graph [-h] -n NIGHT [-o OUTPUT] [-s SPECPROD]

optional arguments:
  -h, --help            show this help message and exit
  -n NIGHT, --night NIGHT
                        night to process
  -o OUTPUT, --output OUTPUT
                        output HTML file (default run/jobgraph/jobgraph-NIGHT.html in reduxdir)
  -s SPECPROD, --specprod SPECPROD
                        override $SPECPROD, or full path to override $DESI_SPECTRO_REDUX/$SPECPROD

[akremin]

This is a handy script for visualizing a night of processing. I am already imagining additional features but I will hold back on that now. I have some comments in-line that would be nice to have addressed before merging. Then we can build up the feature set with future PR's.

[sbailey]

Thanks for the good comments; I believe all are addressed, and a slipped in one more feature of adding a link to the specproddir instead of just the test of the specproddir.

[akremin]

All comments have been resolved. The script looks good and my test run succeeded. I'll approve and merge this now.