Fix docker networking when no reverse-proxy is used

For example, synapse-admin connects to additional networks here:
c0559870b5/roles/custom/matrix-synapse-admin/templates/systemd/matrix-synapse-admin.service.j2 (L39-L41)

This defaults to 'traefik' through
matrix_playbook_reverse_proxy_container_network, which is not correct in
case matrix_playbook_reverse_proxy_type is set to none.

group_vars/matrix_servers

@@ -32,7 +32,7 @@ matrix_playbook_docker_installation_daemon_options_custom: {}
 # yet still use Traefik installed in another way.
 matrix_playbook_traefik_labels_enabled: "{{ matrix_playbook_reverse_proxy_type in ['playbook-managed-traefik', 'other-traefik-container'] }}"
 
-matrix_playbook_reverse_proxy_container_network: "{{ traefik_container_network if traefik_enabled else 'traefik' }}"
+matrix_playbook_reverse_proxy_container_network: "{{ traefik_container_network if traefik_enabled else 'traefik' if matrix_playbook_reverse_proxy_type in ['playbook-managed-traefik', 'other-traefik-container'] else '' }}"
 matrix_playbook_reverse_proxy_hostname: "{{ traefik_identifier if traefik_enabled else 'traefik' }}"
 
 matrix_playbook_reverse_proxy_traefik_middleware_compression_enabled: "{{ traefik_config_http_middlewares_compression_enabled if (traefik_enabled and traefik_config_http_middlewares_compression_enabled) else false }}"

roles/custom/matrix-base/defaults/main.yml

@@ -234,7 +234,7 @@ matrix_metrics_exposure_http_basic_auth_users: ''
 matrix_playbook_reverse_proxy_type: ''
 
 # Specifies the network that the reverse-proxy is operating at
-matrix_playbook_reverse_proxy_container_network: 'traefik'
+matrix_playbook_reverse_proxy_container_network: "{{ 'traefik' if matrix_playbook_reverse_proxy_type in ['playbook-managed-traefik', 'other-traefik-container'] else '' }}"
 
 # Specifies the hostname that the reverse-proxy is available at
 matrix_playbook_reverse_proxy_hostname: 'matrix-traefik'