The Vietnam War is far behind us. Yet director Spike Lee’s latest joint, “Da 5 Bloods,” resonates today with cultural relevance that he could not have anticipated when he boarded a plane to film in Thailand the day after winning a 2019 Oscar for the “BlacKkKlansman” screenplay.A mash-up of “Treasure of the Sierra Madre,” “Apocalypse Now” and “Bloods” — Wallace Terry’s seminal oral history of black Vietnam War veterans — “Da 5 Bloods …