Add note about extended key usage for Logstash output

[kilfoyle]

This adds the note in green to the Configure SSL/TLS for the Logstash output page.

In the docs issue @jguay asked: "Potentially check we use same libbeat code for logstash output managed by fleet so requirements documented for beats would apply equally"

@kpollich Would you be able to help me with Julien's question, i.e, to verify if this requirement applies to the Fleet Logstash output as it does to Filebeat?

Assuming that I should merge this PR, I'll then open another one for the 9.0+ docs.

[github-actions]

A documentation preview will be available soon.

• 🔨 Buildkite builds
• 📚 HTML diff
• 📙 Preview page

Request a new doc build by commenting

• Rebuild this PR: run docs-build
• Rebuild this PR and all Elastic docs: run docs-build rebuild

_{run docs-build is much faster than run docs-build rebuild. A rebuild should only be needed in rare situations.}

_{If your PR continues to fail for an unknown reason, the doc build pipeline may be broken. Elastic employees can check the pipeline status here.}

[github-actions]

Warning

It looks like this PR modifies one or more .asciidoc files. These files are being migrated to Markdown, and any changes merged now will be lost. See the migration guide for details.

[kilfoyle]

@kpollich Would any of the Fleet devs have some time to check on the requirement added here? It's way over my head. :-)

[mergify]

This pull request is now in conflict. Could you fix it @kilfoyle? 🙏
To fixup this pull request, you can check out it locally. See documentation: https://help.github.com/articles/checking-out-pull-requests-locally/

git fetch <remote-repo>
git checkout -b 1757/key-usage-ls <remote-repo>/1757/key-usage-ls
git merge <remote-repo>/main
git push <remote-repo> 1757/key-usage-ls

[kpollich]

Hey @kilfoyle it looks like we missed this PR last year. @juliaElastic @criamico do you have any additional context that might help with getting this closed, or is this no longer relevant?

[juliaElastic]

I don't know, this sounds more like a question to the Agent team cc @ebeahan @cmacknz