Monitor Tor users spikes in prometheus

We should publish our backend csv from meronense as open metrics for prometheus to scrape so we can monitor Tor spikes across countries.

The csv structure is like this:

date,node,country,transport,version,frac,low,high
2022-06-07,bridge,us,<OR>,,89,181,280$
2022-06-07,bridge,us,meek,,89,377,378$
2022-06-07,bridge,us,obfs3,,89,4,5$
2022-06-07,bridge,us,obfs4,,89,5365,5464$
2022-06-07,bridge,us,snowflake,,89,542,543$

This would be a first step towards a detection and notification system of anomalies in Tor and bridge usage (tpo/network-health/team#94)