Expose topic/subscription/consumer number of messages as counter.

[one1zero1one]

Is your feature request related to a problem? Please describe.
Topic metrics are expressed as computed rates, e.g. gauges: pulsar_rate_in pulsar_rate_out. This makes Prometheus scraping miss any change of rate in between the scrape interval.

Describe the solution you'd like
Exposing the metrics as counters instead/in addition to gauges, e.g. pulsar_count_in would allow the rate to be computed in prometheus, and would not miss change of rates within the scraping interval.

Describe alternatives you've considered
Increasing the scrape interval to <15s however it still misses spikes.
I have considered using a sidecar container that would create the counters from gauges, but it adds unwanted complexity.

[sijie]

@one1zero1one I think @PierreZ already added this feature. We will check if it will be released as part of 2.6.0.