[7.17](backport #40238) Go-based changeset definition for MODULE

[mergify]

Proposed commit message

Added MODULE env var definition within mage.
MODULE is set within invoking mage target, if there are changes brought by the PR, instead of calling separate bash-script to evaluate changes and define variable.

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.

Related issues

• Relates: https://github.com/elastic/ingest-dev/issues/3355

Logs

BK builds:

• metricbeat: https://buildkite.com/elastic/beats-metricbeat/builds?branch=oakrizan%3Amage-module-definition
• x-pack/metricbeat: https://buildkite.com/elastic/beats-xpack-metricbeat/builds?branch=oakrizan%3Amage-module-definition
• x-pack/auditbeat: https://buildkite.com/elastic/beats-xpack-auditbeat/builds?branch=oakrizan%3Amage-module-definition

---

This is an automatic backport of pull request #40238 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of cc0bda7 has failed:

On branch mergify/bp/7.17/pr-40238
Your branch is up to date with 'origin/7.17'.

You are currently cherry-picking commit cc0bda7688.
  (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/metricbeat/pipeline.yml
	deleted:    .buildkite/scripts/changesets.psm1
	new file:   dev-tools/mage/module_changeset.go
	modified:   metricbeat/magefile.go
	modified:   x-pack/metricbeat/magefile.go

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   .buildkite/heartbeat/heartbeat-pipeline.yml
	both modified:   .buildkite/x-pack/pipeline.xpack.auditbeat.yml
	both modified:   .buildkite/x-pack/pipeline.xpack.dockerlogbeat.yml
	both modified:   .buildkite/x-pack/pipeline.xpack.metricbeat.yml
	both modified:   .buildkite/x-pack/pipeline.xpack.winlogbeat.yml
	both modified:   x-pack/auditbeat/magefile.go

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

[mergify]

This pull request has not been merged yet. Could you please review and merge it @oakrizan? 🙏

[oakrizan]

PTAL @alexsapran @belimawr @nfritts

[mergify]

This pull request has not been merged yet. Could you please review and merge it @oakrizan? 🙏

[rowlandgeoff]

x-pack.winlogbeat didn't need the BEAT_PATH in the main branch? https://github.com/elastic/beats/blob/main/.buildkite/x-pack/pipeline.xpack.winlogbeat.yml

[oakrizan]

You are right, it shouldn't be there. For x-pack/winlogbeat in Jenkinsfile within 7 steps running mage build unitTest, only 1 has withModule in both main and 7.17 - which seems to be an inconsistency. I have mentioned it here.
Will remove it.

[mergify]

This pull request has not been merged yet. Could you please review and merge it @oakrizan? 🙏