Prime Video’s hit series “Daisy Jones & the Six” — whose last two episodes about a fictional ’70s band will drop on Friday — while pursuing her own very real music career.A few months before the show premiered atop television and music charts, Waterhouse headlined a 22-night tour, including a sold-out show at New York’s Webster Hall. Bathed in purple light and clad in Saint Laurent spandex pants with a high-necked diaphanous blouse, she sang haunting tracks from her debut album, “I Can’t Let Go,” to an adoring crowd that knew the words.“That was one of the greatest nights of my life,” the glamorous 31-year-old tells Alexa.