Update sky subtraction to work across all fiber configurations

Updated sky subtraction code so that it can handle SuNNs data. At the moment, the code works by comparing position of the spot on the detector and provided locations in the 2d psf array and searching for nearest given the `xMaxDistance` parameter (see https://github.com/Subaru-PFS/drp_stella/blob/91432e704b39c1842f109b24e808a34e8332f796/python/pfs/drp/stella/NevenPsfContinued.py#L53). 

We should change the code that it works via a proper fiber identification mechanism, requesting the solutions from the provided array of 2d point spread function via fiber id. This will probably involve some work and planning by both me and price .