The L.A. Opera’s James Conlon works with musicians from the Colburn School and singers from the opera’s Domingo-Thornton Young Artist Program on two operas suppressed by the Nazis. Conlon: The young musicians “are like sponges. And now every one of these young artists is going to know what it’s like to be in one of these operas. They will know there’s a lot of great music to be discovered.”