chore: archive ruby kafka instrumentation

[Karan-05]

Summary

• move ruby_kafka into instrumentation/archive with an explicit 0.25.0 archival release and updated README/links
• remove the gem from instrumentation/all, CI matrices, release automation, and contributor docs so it no longer ships in new releases
• add an instrumentation/archive/README.md section plus top-level docs explaining where archived components live

Testing

• Not run (local Ruby is 2.6.10; the repo now requires >=2.7). Happy to rerun bundle exec rake test TEST=instrumentation/archive/ruby_kafka/**/* once I have a newer Ruby locally if needed.

[linux-foundation-easycla]

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• ✅ login: Karan-05 / name: KARAN ALLAGH (7888880)

[Karan-05]

Hi @thompson-tomo — this follows the component lifecycle you outlined in #1769/#1984 by archiving ruby_kafka, trimming it from releases/CI, and noting the final 0.25.0 release. Let me know if you want any follow-up (e.g., a separate PR for the release tooling).

[Karan-05]

Understood, thanks @thompson-tomo. I’ll hold this until the source URL PR and the deprecation release are merged, then re-open with the archival step.