UPS has won government approval to operate a nationwide fleet of drones, which will let the company expand deliveries on hospital campuses and move it one step closer to making deliveries to consumers. Many regulatory obstacles remain, however, before UPS — or other operators who are testing drones — can fill the sky over cities and suburbs with drones carrying goods to people’s doorsteps. United Parcel Service Inc. said Tuesday that its drone subsidiary was awarded an airline certificate last week by the Federal Aviation Administration, the first U.S. company to get such a broad approval.