add Prow metrics dashboard to grafana

[goern]

Is your feature request related to a problem? Please describe.
Prow is exposing a lot of metrics for example at http://gh-proxy-metrics-opf-ci-prow.apps.smaug.na.operate-first.cloud/metrics please make them available as a grafana dashboard. https://github.com/kubernetes/test-infra/tree/d917e4a1e773ccf701ac58424a0b4ee3490e8dd1/config/prow/cluster/monitoring/mixins/grafana_dashboards might be helpful

Describe the solution you'd like
A grafana dashboard

Describe alternatives you've considered
n/a

Additional context
n/a

[schwesig]

/kind metrics
/kind data-engineer
/kind data-scientist
/area monitoring