Add Hailong Cui as skills Maintainer

[zhichao-aws]

Description

Following the process at https://github.com/opensearch-project/.github/blob/main/RESPONSIBILITIES.md#becoming-a-maintainer, I have nominated and other maintainers have agreed to add Hailong Cui (@Hailong-am) as a co-Maintainer of the skills repository. Hailong has kindly accepted the invitation.

Hailong has been a long-time and consistent contributor to skills since the repo was created.

He built the visualization tool:
#41

He built the painless script tool:
#380

He set up the mocked http server for integ test framework. The http server is used as mocked LLM endpoint by other tools in the repo:
#92

He also actively fixed flaky tests, build errors and CI scripts:
#69
#70
#114
#173
#316
#477

I believe Hailong has already been participating as much or more than many maintainers and would be a valuable addition to the maintainer team.

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

[zhichao-aws]

Please DO NOT merge this PR until it's reviewed by admin team

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.94%. Comparing base (2b76e3c) to head (cb6fcd2).
Report is 39 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main     #484      +/-   ##
============================================
+ Coverage     81.78%   81.94%   +0.15%     
- Complexity      193      281      +88     
============================================
  Files            11       15       +4     
  Lines           961     1407     +446     
  Branches        137      202      +65     
============================================
+ Hits            786     1153     +367     
- Misses          121      176      +55     
- Partials         54       78      +24     

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[opensearch-trigger-bot]

The backport to 2.x failed:

The process '/usr/bin/git' failed with exit code 128

To backport manually, run these commands in your terminal:

# Navigate to the root of your repository
cd $(git rev-parse --show-toplevel)
# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add ../.worktrees/skills/backport-2.x 2.x
# Navigate to the new working tree
pushd ../.worktrees/skills/backport-2.x
# Create a new branch
git switch --create backport/backport-484-to-2.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 42aa0e97db65d1d961d02de1d547e5f9fe9b0c4e
# Push it to GitHub
git push --set-upstream origin backport/backport-484-to-2.x
# Go back to the original working tree
popd
# Delete the working tree
git worktree remove ../.worktrees/skills/backport-2.x

Then, create a pull request where the base branch is 2.x and the compare/head branch is backport/backport-484-to-2.x.