[Feature]: Allow survey index to be either total or retained catch

[k-doering-NOAA]

Explore option to allow a survey index of a fishing fleet to be for either total catch or retained catch. Thanks to Michael Schirripa for the inspiration!

[Rick-Methot-NOAA]

I think the way to do this would be to create a new survey type rather than to try to create a new special code that told SS3 that an obs was for discarded fish. The internal coding to do this should be straightforward.