kotel: optionally only use messaging.kafka.connects.count for connection metrics

[endorama]

This PR follows the discussion in #670.

I added a new struct field, mergeConnectsMeter bool that is manipulated by WithMergedConnectsMeter(), to control whether to use one or 2 metrics to track connection successes/errors.

By default is set to false to retain current behaviour.

When set to true it disables the creation of messaging.kafka.connect_errors.count metric and follows a different path in Meter.OnBrokerConnect. There is some repetition as I wanted to avoid additional allocations when manipulating otel attributes (unfortunately Attribute Sets don't offer a way to add/remove elements from the set).

I added tests for the previous and new behaviour.

Let me know what you think, happy to adjust based on your feedback and thank you for your review!

[endorama]

@twmb I updated the PR to use attribute.Set and fixed the documentation. I also set this ready for review, happy to know what's your opinion!

[endorama]

@twmb as you've seen me moved away from relying on this monitoring plugin for the use case that spawn this contribution but I'm happy to follow along with it. I still think that it aligns better to expectations in the otel ecosystem so I see a benefit. Let me know if you need anything on my side here and thanks for your time!

[twmb]

Looks good to me, I wanted to wait until I finally had time for 1.17 but really that wasn't necessary -- my bad. Anyway, 1.17 is now released, and now I'll release this one too, thank you!

[twmb]

Ah, sorry, mind dropping the go.mod and go.sum changes? I bumped them to latest before 1.17.

[twmb]

Pinging! @endorama I can clone your repo and edit your commit a bit, I'll give it another week or so but if you drop the go.mod and go.sum changes earlier, we can merge and release yours :)

[endorama]

@twmb sorry for the delay! I removed the commit bumping otel (bdbb6e1 (#691)) and rebased onto master so the branch is up to date.

Thanks for the review!