Make prometheus-node-exporter a bit more capable

By running it in a more privileged container with access to the host network stack and such

roles/matrix-prometheus/templates/prometheus.yml.j2

@@ -36,5 +36,5 @@ scrape_configs:
   {% if matrix_prometheus_node_exporter_enabled %}
   - job_name: node
     static_configs:
-      - targets: ['matrix-prometheus-node-exporter:9100']
+      - targets: ['172.18.0.1:9100']
   {% endif %}