CMT announced additional performers and collaborations for the 2020 CMT Music Awards on Oct. 21. Gabby Barrett, Morgan Wallen, Sam Hunt and Shania Twain are slated to perform, while collaborations include Jimmie Allen and Noah Cyrus, Kelsea Ballerini and Halsey, and Luke Combs and Brooks & Dunn. Previously announced performers include Ashley McBryde, Dan +…