Run unconfigured grafana and prometheus containers

Run unconfigured grafana and prometheus containers

Start with `./launch.sh`, tear down with `podman pod rm -f learn-metrics`.

Prometheus explorer at http://localhost:3001 (to avoid port conflict
with Cockpit). It can list or graph simple queries like
`go_memstats_heap_objects` or `go_memstats_heap_objects[5min]`.

Metrics source at <http://localhost:3001/metrics>
<http://metrics-prometheus:9090/metrics> (in grafana container).

Grafana UI at <http://localhost:3000>, log in as admin:foobar. Manually
add Prometheus data source at <http://metrics-prometheus:9090/metrics>.

This fails with "HTTP Error Not Found" with "Server" access (which is
usually what you want -- "Browser" access fails on CORS).