test overlap checker for small dRICH sensor overlaps

- disable all of the dRICH optics except for two sensors, which have a small overlap
- there is at least one such overlap per sector
- these overlaps were not identified by our CI overlap checks, so we
  test again here, with the dRICH restricted to being composed of 2 such
  overlapping sensors
- the overlap are clearly visible in jsROOT (if you zoom in closely);
  see the dRICH-only subsystem view