WASHINGTON — The slogans are familiar: “The Incredible Edible Egg,” “Pork: The Other White Meat,” and “Got Milk?”They’ve all been part of promotional campaigns overseen by the Agriculture Department and paid for by the industries that vote to organize them. While the idea is simple — an industry-wide promotional campaign at no cost to the government — they’ve often generated controversy, been misunderstood and at times have operated with little oversight.The …