[main](backport #41011) Add missing changelog for ES fix.

[mergify]

The changelog for the 8.15.1 bug that causes data ingestion to stop when connections have a transient error was omitted from the 8.15.2 changelog. Add it back.

It was added in a09bd51#diff-867eb8a32d99eda9bb244b7b86d7abd0031618bae71d0276fe139fe697c3063dR71 but we didn't merge 8.15 into #40982 before merging it to pick it up.

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This is an automatic backport of pull request #41011 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of f4fe6ae has failed:

On branch mergify/bp/main/pr-41011
Your branch is up to date with 'origin/main'.

You are currently cherry-picking commit f4fe6aea5c.
  (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)

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   CHANGELOG.asciidoc

no changes added to commit (use "git add" and/or "git commit -a")

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.

[mergify]

backport-8.x has been added to help with the transition to the new branch 8.x.
If you don't need it please use backport-skip label and remove the backport-8.x label.

[mergify]

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