fix(ci): migrate benchmarks to benchmarking-platform trigger

[jbachorik]

What does this PR do?:
Replaces the broken inline benchmark jobs with a benchmarking-platform bridge trigger. The old jobs ran the profiler inline via shell scripts and uploaded results to S3 themselves; the new approach delegates entirely to the BP pipeline at DataDog/apm-reliability/benchmarking-platform@java-profiler.

Motivation:
The existing benchmark CI was broken and unmaintained. The benchmarking-platform provides a reliable, standardised infra for running and tracking reliability benchmarks.

Additional Notes:

• benchmarks-trigger is a GitLab bridge job — it cannot appear in needs: of downstream jobs, so post-benchmarks-pr-comment and publish-benchmark-gh-pages now run in a post-benchmarks stage ordered after benchmarks.
• download-s3-reports.sh fetches reports uploaded by BP under s3://relenv-benchmarking-data/java-profiler/${CI_PIPELINE_ID}/.
• The images.yml include is removed — the BP side manages its own Docker image build.
• jb/bench-memory-limit-fix is superseded by this PR (the memory-heavy aarch64 jobs are gone).
• The BP side implementation is in DataDog/benchmarking-platform PR Run tests on musl aarch64 #190.

How to test the change?:
Push to a branch and verify the GitLab pipeline shows a benchmarks-trigger bridge job that fires the BP downstream pipeline. The post-benchmarks-pr-comment and publish-benchmark-gh-pages jobs should run in the post-benchmarks stage after the trigger completes.

For Datadog employees:

• This PR doesn't touch any of that.
• JIRA: [JIRA-XXXX]

[dd-octo-sts]

CI Test Results

Run: #27787875905 | Commit: aa724d6 | Duration: 16m 2s (longest job)

✅ All 32 test jobs passed

Status Overview

JDK	glibc-aarch64/debug	glibc-amd64/debug	musl-aarch64/debug	musl-amd64/debug
8	-	✅	-	-
8-ibm	-	✅	-	-
8-j9	✅	✅	-	-
8-librca	-	-	✅	✅
8-orcl	-	✅	-	-
11	-	✅	-	-
11-j9	✅	✅	-	-
11-librca	-	-	✅	✅
17	✅	✅	-	-
17-graal	✅	✅	-	-
17-j9	✅	✅	-	-
17-librca	-	-	✅	✅
21	✅	✅	-	-
21-graal	✅	✅	-	-
21-librca	-	-	✅	✅
25	✅	✅	-	-
25-graal	✅	✅	-	-
25-librca	-	-	✅	✅

Legend: ✅ passed | ❌ failed | ⚪ skipped | 🚫 cancelled

Summary: Total: 32 | Passed: 32 | Failed: 0

---

Updated: 2026-06-18 20:58:59 UTC