Version decoupling and tests for MDS

[ansjcy]

Description

Support version decoupling and added unit tests for MDS

• Add a cluster dstest with expected version
• Add another cluster with lower version
• Only dstest is shown on the selector

Issues Resolved

List any issues this PR will resolve, e.g. Closes [...].

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[deshsidd]

LGTM overall

[derek-ho]

LGTM

[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/query-insights-dashboards/backport-2.x 2.x
# Navigate to the new working tree
pushd ../.worktrees/query-insights-dashboards/backport-2.x
# Create a new branch
git switch --create backport/backport-74-to-2.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 53684b1b494b9d4772d88385f148dfa289e0d549
# Push it to GitHub
git push --set-upstream origin backport/backport-74-to-2.x
# Go back to the original working tree
popd
# Delete the working tree
git worktree remove ../.worktrees/query-insights-dashboards/backport-2.x

Then, create a pull request where the base branch is 2.x and the compare/head branch is backport/backport-74-to-2.x.