add listmonk app

modules/apps/listmonk/lib/scripts/create-backup.sh

@@ -0,0 +1,12 @@
+#!/bin/bash
+set -euo pipefail
+
+source /opt/environment/.env
+
+TIMESTAMP=$(date +'%Y-%m-%d_%H%M%S')
+
+systemctl stop listmonk
+sudo -u $USERNAME pg_dump -Fc -U $DB_USER $DB_NAME > $SERVICE_BACKUPS_DIR/$SERVICE_BACKUPS_PREFIX-$TIMESTAMP.$SERVICE_BACKUPS_EXTENSION
+systemctl start listmonk
+
+ls -1dt $SERVICE_BACKUPS_DIR/$SERVICE_BACKUPS_PREFIX-*.$SERVICE_BACKUPS_EXTENSION | tail -n +5 | xargs -r rm -f