[Feature]: Output body weight-at-age of retained and discarded fish when retention function is used

[k-doering-NOAA]

Imported from redmine, Issue #80429 Opened by @RickMethot on 2020-06-30 Status when imported: New

Laura Lee has requested this output The calculations go in function Make_FishSelex()

Also look at how this function does updating in forecast years. It may be storing only in endyr+1

Since this is a frequently called routine, consider making different versions for length selectivity and for discard scenarios

[k-doering-NOAA]

Implies theter is a need for code review here