Racecar consumer instrumentation improvements

[ErvalhouS]

What does this pull request do?

This PR adds better context to Racecar consumer transactions.

1. Transaction naming now includes the consumer class, in a format that is similar to the current Rails instrumentation i.e.: ConsumerClass#method
2. Transaction success/failure based on Racecar's exception handling

Why is it important?

Right now there's only the process.args to differ transactions happening in different consumers, which could be problematic since it isn't the default visualization grouping from other libraries. Error handling is also not recorded, what makes transactions be stored with an unknown status.

Checklist

• I have signed the Contributor License Agreement.
• My code follows the style guidelines of this project (See .rubocop.yml)
• I have rebased my changes on top of the latest main branch
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I have made corresponding changes to the documentation
• I have updated CHANGELOG.asciidoc
• I have updated supported-technologies.asciidoc
• Added an API method or config option? Document in which version this will be introduced

Related issues

Relates #1284

[picandocodigo]

@elasticmachine run elasticsearch-ci/docs

[ErvalhouS]

I don't think the tests failures had anything to do with the changes.

[picandocodigo]

@ErvalhouS thank you for the contribution. No, the build failures are not related to your change. I'm trying to fix the build in a different PR and once that's done, I'll rebase this branch to bring in the changes. Thank you!

[ErvalhouS]

@picandocodigo can we trigger a re-run on CI?

[ronualdo]

Any news on this?

[smith]

@copilot resolve the merge conflicts in this pull request

[smith]

@copilot resolve the merge conflicts in this pull request

[smith]

Please merge latest and fix conflicts so we can review and merge.

[ErvalhouS]

Merged latest main and resolved the conflict — should be ready for review @smith.

There was a single conflict: CHANGELOG.asciidoc was removed upstream by the AsciiDoc → Markdown docs migration (#1516), so the entry moved to docs/release-notes/index.md under a version.next section.

Verified locally on the merge commit:

• FRAMEWORK=rails-7.1 bundle exec rspec spec/elastic_apm/spies/racecar_spec.rb → 4 examples, 0 failures
• bundle exec rubocop lib/elastic_apm/spies/racecar.rb spec/elastic_apm/spies/racecar_spec.rb → no offenses

Two bits of self-review context for whoever picks this up, both intentionally left as-is:

1. The rescue LoadError branches now warn instead of failing silently. That message will print for any app without ActiveSupport loaded, which is a behavior change beyond the scope of the title — happy to drop it if you'd rather keep the load path quiet.
2. record_outcome sets transaction.outcome and calls transaction.done(...), and process_message/process_batch then call ElasticAPM.end_transaction. The second done is a no-op in practice, so the outcome is correct either way, but it's redundant and could be collapsed into ElasticAPM.end_transaction(result).