replace AUTH_FILE with PROMBENCH_GKE_AUTH (#6180)
replace AUTH_FILE with PROMBENCH_GKE_AUTH (#6180)

Signed-off-by: Hrishikesh Barman <0c999f59ffc218332a01ba4bc95df4d1eddc6396@gmail.com>
Gouthamve/prometheus,keegancsmith/prometheus,keegancsmith/prometheus,alileza/prometheus,prometheus/prometheus,GoogleCloudPlatform/prometheus,Gouthamve/prometheus,Gouthamve/prometheus,kangwoo/prometheus,GoogleCloudPlatform/prometheus,GoogleCloudPlatform/prometheus,GoogleCloudPlatform/prometheus,prometheus/prometheus,keegancsmith/prometheus,alileza/prometheus,prometheus/prometheus,alileza/prometheus,prometheus/prometheus,Gouthamve/prometheus,kangwoo/prometheus,GoogleCloudPlatform/prometheus,kangwoo/prometheus,keegancsmith/prometheus,keegancsmith/prometheus,alileza/prometheus,kangwoo/prometheus,alileza/prometheus,prometheus/prometheus