Merge designs from different light sources.

With our current design scheme, when we take darks with spectrograph module connected to different light source we hand up with this :

(rubin3_ics) pfs@shell-ics:/data/raw/2023-01-04/sps$ fitsheader PFSA084574*1.fits|grep 'W_PFD'
W_PFDSGN=           3735928559 / pfsDesign, from sunss                          
W_PFDSGN=        1099528409104 / pfsDesign, from dcb  

Same visit but different designId, which violates the general rule, we actually don't care about the designId, because it's a bias/dark, but it's still need to be unique.

We need to merge those two designs, and probably create a new targetType dcb