Kelsea Ballerini will team with Halsey for the 70th episode of CMT Crossroads. The episode will be taped at Nashville’s Ascend Amphitheater on Oct. 11. The concert is open to the public on a first-come, first-served basis. Doors open at 6 p.m. and close at 7:30 p.m. for the concert that’s slated to end at…