Upgrade Grafana dashboard json to support Grafana 13 (V2 Resource)

The [NixOS foundation Grafana](https://grafana.nixos.org) has been updated to Grafana 13.0.3. Let's update the dashboard in this repo to the [V2 Resource](https://grafana.com/docs/grafana/latest/visualizations/dashboards/build-dashboards/view-dashboard-json-model/#different-dashboard-schema-models) format so it's compatible with Grafana 13+.