Put 2022-09 raster.py and associated notebook in git

We reduced the dithered fields observed during the 2022-09 engineering run using a notebook and a couple of .py files, notably raster.py. Those are on pfsa:/work/

, but need to be cleaned up, merged, and put in some repo.

I believe that the important parts of the notebooks and raster.py are very close. I propose that rhl pins down raster.py, and cloomis pins down his notebook and partial dataset grouping module. Note that these should all be useful for the random dithers.

Not sure where we are putting these kinds of things. pfs_utils is probably not a good place.