Reformat "filepath" keys from ccdActor, etc.

With the /data layout from INSTRM-823, the filepath keyword start looking silly: filepath=/data/pfs/20200506,sps,PFJA05015691.fits. It still works, because os.path.join() works. But it is not ROOT,OBSDATE,FILE.

Since we are using the pfs_utils butler, I think we should add an entirely different key which has the obsDay,visit,prefix,arm,spectrograph components. Maybe explicitly include the root.