feat: include support for metrics

[acuarica]

Description:

This PR adds another endpoint, /metrics, where you can fetch service metrics to be ingested by Prometheus/Grafana.

Using for instance the NodeJS Application Dashboard you can see NodeJS metrics

It also exports requests and events (response) triggered during verification. All requests made to the service (e.g. https://server-verify.hashscan.io/api-docs) will be included, for example

sourcify_http_request_duration_seconds_bucket{le="0.003",status_code="200",method="POST",path="/verify"} 3
sourcify_http_request_duration_seconds_bucket{le="0.03",status_code="200",method="POST",path="/verify"} 4
sourcify_http_request_duration_seconds_bucket{le="0.1",status_code="200",method="POST",path="/verify"} 5
sourcify_http_request_duration_seconds_bucket{le="0.3",status_code="200",method="POST",path="/verify"} 5
sourcify_http_request_duration_seconds_bucket{le="1.5",status_code="200",method="POST",path="/verify"} 6
sourcify_http_request_duration_seconds_bucket{le="10",status_code="200",method="POST",path="/verify"} 6
sourcify_http_request_duration_seconds_bucket{le="+Inf",status_code="200",method="POST",path="/verify"} 6
sourcify_http_request_duration_seconds_sum{status_code="200",method="POST",path="/verify"} 0.632749876
sourcify_http_request_duration_seconds_count{status_code="200",method="POST",path="/verify"} 6

# HELP sourcify_up 1 = up, 0 = not up
# TYPE sourcify_up gauge
sourcify_up 1

# HELP sourcify_event_count events that happened during verification labeled with: event and chainId
# TYPE sourcify_event_count counter
sourcify_event_count{event="Verification.MatchStored",chainId="298"} 2

Note that the sourcify_ prefix is used all metrics to easily differentiate in Grafana.

The events exported are

  "Verification.MatchStored": [],
  "Server.SourcifyChains.Warn": [],
  // [...]
  "SourceFetcher.UsingFallback": [],
  "SourceFetcher.NewSubscription": [],
  "SourceFetcher.Cleanup": [],
  "SourceFetcher.FetchFailed": [],
  "SourceFetcher.FetchingSuccessful": [],

(the ones omitted [...] are Monitor.* related not used at the moment)

Related issue(s):

Fixes #

Notes for reviewer:

Checklist

• Documented (Code comments, README, etc.)
• Tested (unit, integration, etc.)

[Nana-EC]

LG
Just naming suggestion

[AlfredoG87]

LGTM, nice work!

I like that you used the express-prom-bundle and did not had to do things from scratch! 💯

[svienot]

Looks good to me.