feat: add kafka metrics exporter

[Red-GV]

Changes

This PR adds the Kafka metrics exporter to bring in more Prometheus metrics from Kafka.

Merge Requirements

For new features contributions, please make sure you have completed the following
essential items:

• CHANGELOG.md updated to document new feature additions
• Appropriate documentation updates in the docs
• Appropriate Helm chart updates in the helm-charts

Maintainers will not merge until the above have been completed. If you're unsure
which docs need to be changed ping the
@open-telemetry/demo-approvers.

[Red-GV]

Original Request: #3139
Helm Chart PR: open-telemetry/opentelemetry-helm-charts#2125

[cyrille-leclerc]

Thank you for your proposal.
Please review question:

• #3139 (comment)

[Red-GV]

@cyrille-leclerc After some testing, I've gone with the kafkametrics receiver that you pointed me too (thanks for that!). I am in the middle of updating the Helm charts as well to match.

[cyrille-leclerc]

Thanks! I'll test ASAP

PR was updated to use Collector kafkametrics receiver

[cyrille-leclerc]

It doesn't work on my environment

OTelCol error message

2026-04-03T14:57:17.436416250Z 2026-04-03T14:57:17.435Z	error	scraperhelper@v0.146.1/obs_metrics.go:61	Error scraping metrics	{"resource": {"service.instance.id": "ad48bad7-0f36-4a00-a7d6-2519a640bbb7", "service.name": "otelcol-contrib", "service.version": "0.146.1"}, "otelcol.component.id": "kafkametrics", "otelcol.component.kind": "receiver", "otelcol.signal": "metrics", "scraper": "kafkametrics", "error": "franz-go: ListTopics failed: unable to dial: dial tcp :9092: connect: connection refused"}
2026-04-03T14:57:17.436437625Z go.opentelemetry.io/collector/scraper/scraperhelper.wrapObsMetrics.func1
2026-04-03T14:57:17.436440250Z 	go.opentelemetry.io/collector/scraper/scraperhelper@v0.146.1/obs_metrics.go:61
2026-04-03T14:57:17.436441458Z go.opentelemetry.io/collector/scraper.ScrapeMetricsFunc.ScrapeMetrics
2026-04-03T14:57:17.436442667Z 	go.opentelemetry.io/collector/scraper@v0.146.1/metrics.go:24
2026-04-03T14:57:17.436443625Z go.opentelemetry.io/collector/scraper/scraperhelper.scrapeMetrics
2026-04-03T14:57:17.436444583Z 	go.opentelemetry.io/collector/scraper/scraperhelper@v0.146.1/controller.go:167
2026-04-03T14:57:17.436445542Z go.opentelemetry.io/collector/scraper/scraperhelper.NewMetricsController.func1
2026-04-03T14:57:17.436446458Z 	go.opentelemetry.io/collector/scraper/scraperhelper@v0.146.1/controller.go:139
2026-04-03T14:57:17.436447375Z go.opentelemetry.io/collector/scraper/scraperhelper/internal/controller.(*Controller[...]).startScraping.func1
2026-04-03T14:57:17.436448417Z 	go.opentelemetry.io/collector/scraper/scraperhelper@v0.146.1/internal/controller/controller.go:117
2026-04-03T14:57:17.436449417Z sync.(*WaitGroup).Go.func1
2026-04-03T14:57:17.436450250Z 	sync/waitgroup.go:258
2026-04-03T14:57:17.436616167Z 

[cyrille-leclerc]

I understand the bug, let me push a fix