cortex_querier_.* metrics no longer differentiates api/prom/v1 routes

[csmarchbanks]

After deploying 1.5.0-rc.0 I noticed that some of our dashboards broke, upon digging in I noticed that the cortex_querier_.* metrics truncate routes to just api_prom_api_v1 rather than e.g. api_prom_api_v1_query. Metadata is still split into api_prom_api_v1_metadata, but not query, query_range, series, etc...

I think this might be related to #3320, but didn't have time yet to fully dig in.

@jtlisi would you be able to see if it is related to #3320?

[jtlisi]

I believe it is related to #3320, it included a change meant to simplify route registration by using a PathPrefix to register the Prometheus API handler for all of the routes instead of registering them explicitly. /metadata and /read will still work because they registered explicitly still.

router.PathPrefix(cfg.PrometheusHTTPPrefix + "/api/v1/").Handler(promRouter)

[jtlisi]

Fixed in #3436