Telegraf (on any host) collecting data from Grafana's native (on by default) Prometheus endpoint
Push them to InfluxDB OSS 2.x (tested on v2.3)
Same or other Grafana allow you to choose any flux-compartible datasource and show basic stats, aggregated over variable-defined intervals

I don't use proxy right now, so this part is not finished. But you can re-use "Dashboards X Stats" pattern to get same result.

Collector Configuration Details

[[outputs.influxdb_v2]] 
  urls = ["$INFLUX_HOST"]
  token = "$INFLUX_TOKEN"
  bucket = "$INFLUX_BUCKET"
  organization = "$INFLUX_ORG"
  influx_uint_support = true

## Grafana OSS specific metrics
[[inputs.prometheus]]
  urls = ["https://HOSTNAME/metrics"]
  insecure_skip_verify = true
  [inputs.prometheus.tags]
    host = "HOSTNAME"