Narrow example JMX exporter rules for socket, raft-channel and RequestMetrics

[guancioul]

Type of change

• Enhancement / new feature

Description

Following the metrics survey and discussion in #10188, this narrows the example JMX Prometheus Exporter rules (packaging/examples/metrics/kafka-metrics.yaml) to only export the metrics actually used by the shipped Grafana dashboards and Prometheus alert rules:

• socket-server-metrics: keep only connection-count, drop the rest.
• raft-channel-metrics: keep only incoming-byte-total, outgoing-byte-total, request-total, response-total.
• Exclude RequestMetrics entirely from the generic catch-all rules (contributed ~22 unused metric types).

The Strimzi Metrics Reporter example (packaging/examples/metrics/strimzi-metrics-reporter/kafka-metrics.yaml) is intentionally left untouched, its allowList mechanism is allow-only (no deny), so matching this exclusion needs a different approach and will be addressed separately.

AI assistance disclosure: Claude Code was used to help draft the narrowed regex rules and to run local verification (spinning up real Kafka brokers via Docker with the old/new JMX exporter config and diffing the scraped metrics). I reviewed all changes, understand them, and can answer questions about them.

Checklist

• Reference relevant issue(s) and close them after merging
• Try your changes inside a Kubernetes cluster, not just from unit tests
• AI assistance was used to create this PR (see the Strimzi AI policy)

[snyk-io]

✅ Snyk checks have passed. No issues have been found so far.

Status	Scan Engine	Critical	High	Medium	Low	Total (0)
✅	Open Source Security	0	0	0	0	0 issues
✅	Licenses	0	0	0	0	0 issues
✅	Code Security	0	0	0	0	0 issues

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.89%. Comparing base (0b52fda) to head (4704a89).
⚠️ Report is 43 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main   #13139      +/-   ##
============================================
+ Coverage     80.58%   80.89%   +0.31%     
- Complexity     6581     6738     +157     
============================================
  Files           344      355      +11     
  Lines         22777    23072     +295     
  Branches       3111     3148      +37     
============================================
+ Hits          18355    18665     +310     
+ Misses         3204     3180      -24     
- Partials       1218     1227       +9     

see 47 files with indirect coverage changes

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[scholzj]

Great, thanks for the PR.