Made optional fields optional, added tests to check for them

refs #16653
Changed optional field tests to be more general, and test for blanks

refs #16653
Added more optional fields

refs #16653

Updated image_id and link in product, and phone, lat, long, and story in vendor.
Remove null=True where not required
Merge branch 'feature/16653' into develop
Merge branch 'develop' of github.com:osu-cass/whats-fresh-api into develop