Marijuana has long been accused of being a gateway to deadlier vices. But could cannabis be a swinging door that might also lead people away from hard drugs? That’s what this capital city is trying to find out. In coming weeks, Bogotá is embarking on a controversial public health project where it will begin supplying marijuana to 300 addicts of bazuco — a cheap cocaine derivative that generates crack-like highs and is as addictive as heroin.