Try to tighten Signal bridge security

roles/matrix-bridge-mautrix-signal/templates/systemd/matrix-mautrix-signal.service.j2

@@ -24,6 +24,8 @@ ExecStart={{ matrix_host_command_docker }} run --rm --name matrix-mautrix-signal
 			--log-driver=none \
 			--network={{ matrix_docker_network }} \
 			--user={{ matrix_user_uid }}:{{ matrix_user_gid }} \
+			--cap-drop=ALL \
+			--read-only \
 			{% if matrix_mautrix_signal_container_http_host_bind_port %}
 			-p {{ matrix_mautrix_signal_container_http_host_bind_port }}:29328 \
 			{% endif %}