feat(prometheus): Include tags in metrics labels

[carnei-ro]

Moving https://github.com/Kong/kong-plugin-prometheus/pull/149 to here

closes https://github.com/Kong/kong/issues/7678

[rmrf]

how this going

[mayocream]

@carnei-ro hi, any updates?

[carnei-ro]

hey guys, I'm not really sure why some tests are failing - need help

[mayocream]

Hi @carnei-ro

IMO, I don't think this behavior should be included in promethues plugin officially.

1. We might want to avoid adding empty labels like service_tags="",route_tags="" by default
2. Don't overuse labels, cardinality can be very large

ref:

• https://github.com/prometheus/consul_exporter/issues/45

[hbagdi]

We won't be able to accept this contribution at this point. The cardinality issues in the plugin have been plaguing Kong's performance for quite some time. Please revisit this change in 6 months.