Clover Sonoma, the North Bay dairy, has jumped on a trend of companies using pop-ups — temporary stores that offer flash sales or distinctive experiences — to generate some extra attention. For the next month, the Clover Sonoma Milk tasting room will employ contracted milk sommeliers — or “somoo’liers,” as the company prefers — who walk customers through the nuances of different kinds of milk, from low-fat to whole.