Add the possibility to pass extra flags to the docker container

roles/matrix-mxisd/templates/systemd/matrix-mxisd.service.j2

@@ -27,6 +27,9 @@ ExecStart=/usr/bin/docker run --rm --name matrix-mxisd \
 			{% endif %}
 			-v {{ matrix_mxisd_config_path }}:/etc/mxisd:ro \
 			-v {{ matrix_mxisd_data_path }}:/var/mxisd:rw \
+			{% for arg in matrix_mxisd_container_extra_arguments %}
+			{{ arg }} \
+			{% endfor %}
 			{{ matrix_mxisd_docker_image }}
 
 ExecStop=-/usr/bin/docker kill matrix-mxisd