Comply with the root agent id config change in dashboards-assistant

[SuZhou-Joe]

Description

opensearch-project/dashboards-assistant#127
In dashboard-assistant repo, we changed the implementation of how to retrieve the root agent id.

Issues Resolved

[List any issues this PR will resolve]

Check List

• Commits are signed per the DCO using --signoff

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.

[SuZhou-Joe]

A test case is flaky because of the opensearch-project/ml-commons#1894, I intentionally add a test to see if the suggestions returns stable.

[opensearch-trigger-bot]

The backport to main 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-main main
# Navigate to the new working tree
cd .worktrees/backport-main
# Create a new branch
git switch --create backport/backport-1053-to-main
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 7625e0074a4e684ce521f71503756b4b6aa23910
# Push it to GitHub
git push --set-upstream origin backport/backport-1053-to-main
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-main

Then, create a pull request where the base branch is main and the compare/head branch is backport/backport-1053-to-main.