backend-utils: Make script verbose

Refs. swh/infra/sysadm-environment#5608

swh/templates/utils/backend-utils.yaml

@@ -173,6 +173,8 @@ data:
         echo "Datasets graph & provenance <${DATASET_VERSION}> already present. Skip." && \
         exit 0
 
+    set -x
+
     URL_PROVENANCE="s3://softwareheritage/derived_datasets/${DATASET_VERSION}/provenance/all/"
 
     CMD_GET="aws s3 cp --no-sign-request"