Songwriter Katie Gavin broke big in 2022 as a member of MUNA. The indie-pop trio’s joyous post-major-label, self-titled release landed the band in exalted territory, on stage with Taylor Swift and boygenius. With “Aftertaste,” Gavin has shared a preview of her debut solo effort, What A Relief. The acoustic-forward love song stands on a solid foundation of ‘90s-pop-radio production, a …