Use Grafana's new 'State timeline' visualization in Grafana 8.0 for uptime

See: https://grafana.com/docs/grafana/latest/panels/visualizations/state-timeline/

Right now the dashboard uses a 3rd party plugin, but it has some issues like https://github.com/geerlingguy/internet-monitoring/issues/8 — maybe this 1st-party graph type will resolve that issue?