GFA_TARGETS GUIDE/FOCUS/ETC_FLAG updates

[sbailey]

Currently the GUIDE_FLAG, FOCUS_FLAG, and ETC_FLAG values in the GFA_TARGETS table are just point-source cuts. 0=good, and non-zero flags why it wasn't selected. Define specific bits, adding:

• NOT_ISOLATED: isolation cuts
• WRONG_GFA_TYPE:
  • targets on Guider GFAs shouldn't be used for focus, and vice-a-versa
  • targets on focus GFAs shouldn't be used for ETC
• TOO_BRIGHT: Too bright (value TBD)
• BAD_ASTROMETRY: cuts TBD, e.g. cuts on astrometric_excess_noise, or Tycho2 stars not matched to Gaia.

GFA_LOC for guide GFAs: 0, 2, 3, 5, 7, 8

GFA_LOC for focus GFAs: 1, 4, 6, 9

From DESI-0742 (G=guide, W=wavefront sensor = focus)