Make non-lens catalog more realistic using DC2 data

[jiwoncpark]

Right now, the non-lens catalog consists of single Gaussian SDSS galaxies. Would like to use DC2 data to replace them with multiple Sersic galaxies.

[jiwoncpark]

Specifying sub-tasks here: (Branched off) #55

• [ ] Get which "quantities" for GCR
• [ ] Fetch the full cosmoDC2 v2.0 catalog (not just image field) from GCR. Note the "lens" CosmoDC2Realizer will need the full and the Sprinkler validation will just need the image field. I've already edited out the slicing and size printing.
• [ ] Use Butler to access a sample src catalog
• [ ] Check # of visits, # galaxies, and column values in the src catalog
• [ ] Check how many AGNs and where in the cosmoDC2 AGN DB
• [ ] Apply the matching to cosmoDC2 AGN DB
• [ ] Ask Phil (+ Scott?) about the lack of galactic sources