Add a specification of the 1-D PSF to pfsArm and pfsObject files

The DRP-2D defines the 2-D PSF for every pfsArm file, but we also need to know the PSF for the pfsObject file (i.e. the 2-D PSF for all the pfsArm files, as extracted to 1-D using the same algorithm as the object extraction – also called the Line Spread Function, LSF).

I propose adding another HDU to the pfsArm and pfsObject files to capture the LSF as a function of wavelength.