[8.13](backport #4022) Add nginx tutorial to navigation

[mergify[bot]]

Replacing the nav links to the nginx tutorial.

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This is an automatic backport of pull request #4022 done by Mergify.

[mergify[bot]]

Cherry-pick of 57061e02dab5460dc7f61df6986300532f56df53 has failed:

On branch mergify/bp/8.13/pr-4022
Your branch is up to date with 'origin/8.13'.

You are currently cherry-picking commit 57061e02.
  (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:   docs/en/observability/tutorials.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

[github-actions[bot]]

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[mergify[bot]]

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