Watch out, BPS students — researchers will be digging through cafeteria trash to see if you’re eating your vegetables!Boston Public Schools is looking to spend up to $40,000 in grant money on a “plate waste study” designed to see if students are actually eating the food they take in the cafeteria, according to a request for proposals released this week.The study will focus particularly on fruits and vegetables and whether officials can push kids to eat more healthy foods through different menus and other changes.