feat: metrics for request number per route

[Garrethta]

No description provided.

[SkeLLLa]

Hi. Can you elaborate a bit why do you need a dedicated counter? I'm asking since histogram and summary metrics already expose counter as well. So you can reuse it.

[Garrethta]

Hi. Our API consists of routes belonging to different parts of the system that sometimes experience abnormal request amount spikes. A summary metric does not give us information about which route, or group of routes, is under pressure rn and which part of system needs scaling. This pr is an impl of counter metric from this lib but with prom interface.

[SkeLLLa]

@Garrethta currently the following metrics are exposed:

          'http_request_duration_seconds_count{method="GET",route="/test",status_code="200"} 1',
          'http_request_duration_seconds_count{method="POST",route="/test",status_code="200"} 1',
          'http_request_summary_seconds_count{method="GET",route="/test",status_code="200"} 1',
          'http_request_summary_seconds_count{method="POST",route="/test",status_code="200"} 1',

Your PR adding a new metric that looks like:

          'route_request_counter{route="/test",status_code="200"} 2'

So my point is why not to use prometheus function like sum (http_request_summary_seconds_count) by (route, status_code) which will give you exactly the same numbers as added metric.