Mike Cooley, Patterson Hood, and Jason Isbell in The Secret to a Happy Ending, Barr Weissman’s “love letter to rock and roll,” starring the Drive-By Truckers. It’s been nearly a decade since Southern Rock Opera — a perceptive, engrossing, and very loud meditation on Lynyrd Skynrd, race relations, and growing up and getting out — brought the Pitchfork crowd into the ever-broadening tent of Athens, GA’s Drive-By Truckers. Maryland-based documentarian Barr Weisman’s new DBT…