Allow host network mode for MDAD-managed containers (#5310)

* feat: support container_network=host across all roles + systemd templates

Mirror the pattern Slavi introduced for matrix-coturn (aafa8f0) across the
fork: every 'Ensure X container network is created' task gets a
'when: <var> not in ["", "host"]' guard so MDAD does not try to
docker_network create a network literally named 'host' (returns 403,
since host is a pre-defined Docker network).

Mirror the same guard in every systemd unit template that does
'ExecStartPre=docker network connect <addnet> <container>' loops over
matrix_<role>_container_additional_networks: skip the connects when the
container is on host networking (where additional --network attaches
are invalid).

Unblocks DiD setups where MDAD-managed containers share their host's
network namespace (matrix-mdad outer compose service joined to central
postgres/openldap networks) to reach external services on the outer
Docker daemon.

* Simplify container network guards (!= 'host') and fix duplicate when

Guarding on the empty string ('') as well was misleading: systemd unit
templates still render an unconditional --network= flag, so an empty
network value produces a broken docker create command. Only 'host' is
actually supported, so only guard on that. This also matches the
existing convention in the Traefik role
(when: traefik_container_network != 'host').

Also fix a duplicate when key in the meshtastic-relay role, where the
network-creation task already had a when condition - the two are now
combined into a list.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

---------

Co-authored-by: Slavi Pantaleev <slavi@devture.com>
Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

roles/custom/matrix-client-element/templates/systemd/matrix-client-element.service.j2

@@ -52,9 +52,11 @@ ExecStartPre={{ devture_systemd_docker_base_host_command_docker }} create \
 			{% endfor %}
 			{{ matrix_client_element_container_image }}
 
+{% if matrix_client_element_container_network != 'host' %}
 {% for network in matrix_client_element_container_additional_networks %}
 ExecStartPre={{ devture_systemd_docker_base_host_command_docker }} network connect {{ network }} matrix-client-element
 {% endfor %}
+{% endif %}
 
 ExecStart={{ devture_systemd_docker_base_host_command_docker }} start --attach matrix-client-element