New Mexican award-winning recording artist and composer Randy Granger, who lives in Las Cruces, typically tours the country in a white van loaded with instruments and boxes of CDs, serving as his own publicist and tour manager. This spring, he got a major break: A commission to provide six songs for Ken Burns’ newest documentary. Burns’ documentaries and miniseries including “The Civil War” have reaped Emmys, Grammys and numerous …