Properly specify external network in Docker compose

Pre-existing networks (defined elsewhere) are
marked as `external` in `docker-compose.yml`.

Instead of using `external` as a separate-line key:
```yml
networks:
  service:
    external:
      name: hpcservice_service
```
we should define network by its name and specify
its externality by using `external: true`:
```yml
networks:
  service:
    name: hpcservice_service
    external: true
```

Official docs:
https://docs.docker.com/compose/networking/#use-a-pre-existing-network

By correctly specifying `external` property, we get
rid of warning "network service: network.external.name
is deprecated in favor of network.name". Useful link:
docker-archive/compose-cli#1856 (comment)

docker-compose.integrated.yml

@@ -32,5 +32,5 @@ services:
           - api.hpc.vm
 networks:
   service:
-    external:
-      name: hpcservice_service
+    name: hpcservice_service
+    external: true