added external network for prom pushgw

docker-compose.yml

@@ -25,3 +25,8 @@ services:
       - BORG_SOURCE_PATH=${BORG_SOURCE_PATH}
       - BORG_RETENTION=${BORG_RETENTION}
       - CRON=${CRON}
+    networks:
+      - prometheus_pushgateway
+networks:
+  prometheus_pushgateway:
+    external: true