[backport-gcp-2.22] Sync CI configuration with main branch

[mrodm]

TL;DR

Syncs .buildkite and .github CI configuration from main to the
backport-gcp-2.22 backport branch.

This brings automated backport workflows, new CI scripts, Go tooling, and
GitHub Actions that only work when they are present on the target branch itself.

What does this PR do?

Syncs the following CI configuration from main onto the backport-gcp-2.22\ branch:

• Buildkite — updated hooks (post-checkout, pre-command, pre-exit), pipeline definitions (backport dispatch, publish, schedule-daily, schedule-weekly, serverless, main), and pull-requests.json; adds new scripts for backport orchestration, changelog checks, owner validation, and parallel triggering
• GitHub Actions — adds workflows for auto-backport, post-backport checklist, changelog sync, package docs validation, dashboard YAML validation, sweep workflows (field mapping conflicts, ingest pipeline safety, httpjson pagination, pipeline error handling, dashboard data scope), Vale linting, docs build/deploy/preview, and various trigger/patrol workflows
• Go tooling — cmd/backport sub-module with the full backport apply/changelog/checklist/inventory/owners/packages logic and its test suite; dev/ tooling additions (citools, coverage, packagenames, gitutil, scripts)
• Root module — go.mod/go.sum updates, magefile.go additions, .gitignore updates

GitHub Actions resolves workflow files from the branch where the event occurs, not from main. Backport-branch workflows (changelog sync, post-backport checklist, owner checks, auto-backport) must be present on the backport branch itself to fire correctly.

Proposed commit message

Sync CI configuration with main branch for backport-gcp-2.22.

Keep CI pipelines, GitHub Actions, and tooling consistent between active backport
branches and `main`, so that automated backport workflows and tooling improvements
land on all supported branches.

WHY:
GitHub Actions resolves workflow files from the branch where the event occurs,
not from `main`. Backport-branch workflows (changelog sync, post-backport
checklist, owner checks, auto-backport) must be present on the backport branch
itself to fire correctly.

Author's Checklist

• CI configuration files have been synced verbatim from main.

Related issues

• Relates backport: deploy backport-branch automation workflows to active backport branches #19262

---

This PR was generated with the assistance of Claude (claude-sonnet-4-6).

[elastic-vault-github-plugin-prod]

🚀 Benchmarks report

To see the full report comment with /test benchmark fullreport

[infra-vault-gh-plugin-prod]

💔 Build Failed

• Buildkite Build
• Commit: 9e125e2

Failed CI Steps

• Check integrations activemq
• Check integrations apache
• Check integrations aws
• Check integrations cisco_nexus
• Check integrations cloud_security_posture
• Check integrations entityanalytics_okta
• Check integrations etcd
• Check integrations hadoop
• Check integrations haproxy
• Check integrations jolokia
• Check integrations lmd
• Check integrations logstash
• Check integrations microsoft_sqlserver
• Check integrations nginx
• Check integrations php_fpm
• Check integrations prometheus_input
• Check integrations sentinel_one_cloud_funnel
• Check integrations system
• Check integrations websphere_application_server

History

• 💚 Build #47292 succeeded 0df32b3
• 💔 Build #47287 failed 9bf4adb
• 💔 Build #47285 failed 2468cfc

cc @mrodm