Fix typo in Derived field type

[johtani]

Description

Fix typo in the logs index mappings.
"client_ip" -> "clientip"

Issues Resolved

n/a

Version

2.15-

Frontend features

n/a

Checklist

• By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license and subject to the Developers Certificate of Origin.
  For more information on following Developer Certificate of Origin and signing off your commits, please check here.

[github-actions]

Thank you for submitting your PR. The PR states are In progress (or Draft) -> Tech review -> Doc review -> Editorial review -> Merged.

Before you submit your PR for doc review, make sure the content is technically accurate. If you need help finding a tech reviewer, tag a maintainer.

When you're ready for doc review, tag the assignee of this PR. The doc reviewer may push edits to the PR directly or leave comments and editorial suggestions for you to address (let us know in a comment if you have a preference). The doc reviewer will arrange for an editorial review.

[kolchfa-aws]

Thank you, @johtani!

[opensearch-trigger-bot]

The backport to 2.16 failed:

The process '/usr/bin/git' failed with exit code 1

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add ../.worktrees/backport-2.16 2.16
# Navigate to the new working tree
pushd ../.worktrees/backport-2.16
# Create a new branch
git switch --create backport/backport-7986-to-2.16
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 e5c6395507d12f0c3ec8ce681f9be5e5d9c0ecd0
# Push it to GitHub
git push --set-upstream origin backport/backport-7986-to-2.16
# Go back to the original working tree
popd
# Delete the working tree
git worktree remove ../.worktrees/backport-2.16

Then, create a pull request where the base branch is 2.16 and the compare/head branch is backport/backport-7986-to-2.16.