Improve networks

Create a single external network called "external".
Create container-specific networks.
Only a few containers need access to these.
So far: openldap, postgres.

roles/portainer/tasks/main.yml

@@ -3,8 +3,7 @@
     name: 'portainer'
     image: portainer/portainer-ce
     networks:
-      - name: nginx-internal
-      - name: bridge
+      - name: external
     volumes:
       - "/var/run/docker.sock:/var/run/docker.sock"
     ports: