Prometheus stats on ops per second per pipeline

[johnhtodd]

Is your feature request related to a problem? Please describe.
There is a general counter (per stream) of "dnscollector_throughput_ops" and "dnscollector_throughput_ops_max". This may not make sense in a pipeline model and is too broad to capture meaningful data that is useful for diagnosing how flows are operating within go-dnscollector, and it would be very helpful to understand what the throughput was per pipeline stanza.

Describe the solution you'd like
Using the config file from #510 this is what perhaps the sections would look like:

dnscollector_throughput_ops_max{pipeline="all-data"} 3395
dnscollector_throughput_ops{pipeline="all-data"} 1943
dnscollector_throughput_ops_max{pipeline="apple-only"} 5
dnscollector_throughput_ops{pipeline="apple-only"} 2
dnscollector_throughput_ops_max{pipeline="outputfile"} 3390
dnscollector_throughput_ops{pipeline="outputfile"} 1934
dnscollector_throughput_ops_max{pipeline="dnsdist-receiver-from-prod-machines"} 3395
dnscollector_throughput_ops{pipeline="dnsdist-receiver-from-prod-machines"} 1943

Describe alternatives you've considered
No other alternatives seem viable.

[dmachard]

It will be implemented in next release with global prometheus metrics. More details on PR #724