ci: declare FLAKY_BENCHMARKS_REGEX and document benchmarks CI

[igoragoli]

Overview

• Declare an empty FLAKY_BENCHMARKS_REGEX in the .benchmarks template, linked to Flaky Benchmarks Monitoring.
  • A scenario matching it still runs and reports, but doesn't fail the gate.
• Add .gitlab/BENCHMARKS.md with the benchmarks CI layout and how to mark a benchmark as flaky.

Motivation

APMSP-3925 Onboard dd-trace-* and nginx-datadog to benchmark stability monitoring

Testing

YAML parses. Runs are unchanged since the declared value is empty.

[datadog-official]

✅ All CI checks and tests passed.

🎉 All green!

🧪 All tests passed
❄️ No new flaky tests detected

🎯 Code Coverage (details)
• Patch Coverage: 100.00%
• Overall Coverage: 69.29% (+0.08%)

_{This comment will be updated automatically if new data arrives.
🔗 Commit SHA: 1f4b23f | Docs | View more details | Give us feedback!}

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-09-29T09:57:04.290152Z	295114c	Draft marked ready
🔒 Security Review	✅ Completed 2026-09-29T09:58:03.349104Z	295114c	Draft marked ready

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review" or "@codex security review".

Codex reacts with 👀 while any review is running, comments if it has suggestions, and reacts with 👍 once all reviews finish with no findings.

[xlamorlette-datadog]

Please apply the same tiny corrections as in DataDog/dd-trace-cpp#371.

[igoragoli]

/merge

[gh-worker-devflow-routing-ef8351]

View all feedbacks in Devflow UI.

2026-10-02 07:56:08 UTC ℹ️ Start processing command /merge

---

2026-10-02 07:56:15 UTC ℹ️ MergeQueue: Pull request is not mergeable yet

It will be processed automatically as soon as GitHub reports it as mergeable. View in MergeQueue UI.

• Run /code blockers to see what is blocking it.
• Run /remove to cancel it.

---

2026-10-02 08:59:09 UTC ℹ️ MergeQueue: merge request added to the queue

The expected merge time in master is approximately 0s (p90).

---

2026-10-02 09:28:14 UTC ℹ️ MergeQueue: This merge request was merged