[7.17](backport #38783) Single pipeline entrypoint

[mergify]

Proposed commit message

A single pipeline entry point that triggers other pipelines according to the changeset.
The Main pipeline triggers corresponding pipelines: Auditbeat and Heartbeat.

the statuses are reported back to GH (Simply auditbeat and heartbeat) :

Labels and other critical env vars are passed to the trigger step

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in CHANGELOG.next.asciidoc or CHANGELOG-developer.next.asciidoc.

Author's Checklist

• [ ]

How to test this PR locally

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---

This is an automatic backport of pull request #38783 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of d0a3b45 has failed:

On branch mergify/bp/7.17/pr-38783
Your branch is up to date with 'origin/7.17'.

You are currently cherry-picking commit d0a3b457ec.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   .buildkite/hooks/pre-command
	modified:   .buildkite/pull-requests.json

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   .buildkite/auditbeat/auditbeat-pipeline.yml
	both modified:   .buildkite/heartbeat/heartbeat-pipeline.yml
	both modified:   .buildkite/pipeline.yml
	both modified:   .buildkite/scripts/common.sh

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[botelastic]

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[elasticmachine]

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[pierrehilbert]

You need to fix the conflict

[dliappis]

There are left overs from conflicts e.g. https://github.com/elastic/beats/pull/38793/files#diff-3ad1ceaa38f7134b9714754e777ce9fc4e20aad700f3ea5cfbae253a095f8794R6

hence requesting changes

[pazone]

Resolved

[dliappis]

LGTM

[pazone]

@pierrehilbert It's resolved