backup/restore: use MONGO_SERVICE variable for service name

backup.sh

@@ -1,8 +1,11 @@
 #!/usr/bin/env bash
 set -euo pipefail
 
+# Configuration
+MONGO_SERVICE="utility-bills-tracker_mongo"
+
 # scale down mongo service while we copy its volume
-docker service scale utility-bills-tracker_mongo=0
+docker service scale "$MONGO_SERVICE"=0
 
 # timestamp for filename
 TIMESTAMP=$(date +"%Y-%m-%d-%H-%M")
@@ -30,4 +33,4 @@ if [ "$KEEP" -gt 0 ]; then
 fi
 
 # bring mongo service back up
-docker service scale utility-bills-tracker_mongo=1
+docker service scale "$MONGO_SERVICE"=1