Trending on Billboard At country music festival Stagecoach last month, one of the fest’s most-watched artists wasn’t even officially on the bill. Country-pop artist Stella Lefty, whose breakthrough hit “Boston” has reached No. 27 on the Billboard Hot 100 and the No. 7 on Hot Country Songs, was seemingly everywhere during the weekend, jumping up onstage with artists including Cameron Whitcomb and Wyatt Flores. “I’m a huge fan of Wyatt and also Cam,” she says. “It’s so crazy to be so embraced in a genre that I’ve always loved. Country music has been such a huge part of my life. And I feel like it’s always scary when you start making music that kind of bleeds into a genre.…