fix: request metrics

[nipsufn]

http_request_* metrics contain data related only to /metrics/prometheus endpoint.
This PR adds endpoints from non-monitoring routers.

Related issue(s)

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Further Comments

[hperl]

Thanks for the PR! Do you think it makes sense to add the tracing for gRPC as well, or was that already enabled?

[nipsufn]

GRPC request metrics are not implemented yet, I'll see about adding them.

[hperl]

Hi, thanks, looks good for HTTP traffic. In Cloud Keto is 100% HTTP/REST right now, but we want to change that in the future.

Do we have any way to test that the Prometheus metrics are correctly exposed here? Or are the E2E tests in Cloud anyways?

[nipsufn]

I've added test similar to those we have in other applications. More metric related tests are done on x repo, I think this should be OK for what we are doing.