BRILLIANT ideas sometimes arise out of pure necessity. Consider Piero Lugano, 63, the suntanned artist-turned-wine-merchant who opened a shop called Bisson in this town on the Italian Riviera in 1978. Not content merely to sell wine, he soon began making it. Ten years ago he decided to try producing sparkling wine from indigenous varieties grown in vineyards overlooking the Golfo Paradiso on the Mediterranean.