pretalx: set custom docker network in compose file

resources/chaosknoten/pretalx/docker_compose/compose.yaml.j2

@@ -11,12 +11,16 @@ services:
     volumes:
       - database:/var/lib/postgresql/data
     restart: unless-stopped
+    networks:
+      - pretalx_net
 
   redis:
     image: redis:latest
     restart: unless-stopped
     volumes:
       - redis:/data
+    networks:
+      - pretalx_net
 
   static:
     image: docker.io/library/nginx
@@ -25,6 +29,8 @@ services:
       - public:/usr/share/nginx/html
     ports:
       - 8081:80
+    networks:
+      - pretalx_net
 
   pretalx:
     image: pretalx/standalone:latest
@@ -67,6 +73,8 @@ services:
     volumes:
       - pretalx:/data
       - public:/public
+    networks:
+      - pretalx_net
 
   celery:
     image: pretalx/standalone:latest
@@ -99,9 +107,19 @@ services:
     volumes:
       - pretalx:/data
       - public:/public
+    networks:
+      - pretalx_net
 
 volumes:
   database: {}
   redis: {}
   pretalx: {}
   public: {}
+
+networks:
+  pretalx_net:
+    ipam:
+      driver: default
+      config:
+        - subnet: 172.18.0.0/16
+          gateway: 172.18.0.1