[8.16](backport #42682) x-pack/filebeat/input/entityanalytics/provider/activedirectory: fix use before init bug

[mergify]

Proposed commit message

x-pack/filebeat/input/entityanalytics/provider/activedirectory: fix use before init bug

The transaction tracker was not being initialised until after the first
call to publishMarker in runFullSync, resulting in a nil pointer
deference when the the tracker Add method is called.

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.

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Author's Checklist

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---

This is an automatic backport of pull request #42682 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of 1473ae9 has failed:

On branch mergify/bp/8.16/pr-42682
Your branch is up to date with 'origin/8.16'.

You are currently cherry-picking commit 1473ae916.
  (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:   CHANGELOG.next.asciidoc

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   x-pack/filebeat/input/entityanalytics/provider/activedirectory/activedirectory.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

[botelastic]

This pull request doesn't have a Team:<team> label.

[efd6]

Not relevant for this version.