Use BUILD_TAG if set, else fallback to BUILD_DATE

.gitlab-ci.yml

@@ -38,7 +38,8 @@ workflow:
 
 .get_build_date: &get_build_date
   - export BUILD_DATE=$(TZ=America/Chicago date +%Y-%m-%dT%H%M%S)
-  - echo BUILD_DATE=${BUILD_DATE}
+  - export FINAL_BUILD_TAG=${BUILD_TAG:-$BUILD_DATE}
+  - echo FINAL_BUILD_TAG=${FINAL_BUILD_TAG}
 
 .update_ansible_repo: &update_ansible_repo
   - *get_build_date