Country singer Jessie James Decker is set to join season 31 of “Dancing With The Stars.” The cast of season 31 of “Dancing with the Stars” was revealed on “Good Morning America” on Thursday, September 8. The cast also includes “American Idol” winner Jordin Sparks, “RuPaul’s Drag Race” contestant Shangela, Charli D’Amelio and her mom,…