Introduce execution_hint for Cardinality aggregation

[asimmahmood1]

Description

Introduce execution_hint for Cardinality aggregation - Revive PR #15764

This is intended as short term solution as a workaround to users that see large latency regression when upgrading to OS 2.x. The main risk here is ordinals take up more memory, i.e. depends on size of cardinality. So for very high cardinality, there is a risk of OOM at shard node. This is marked as power user.

I plan to follow up with #15269 which is more useful setting. This will allow the user select a higher threshold for using ordinals, e.g. a shard with large heap can use ordinals more often, but still fall back to the slower direct as needed.

Related Issues

Resolves #16837.

Check List

• Functionality includes testing.
• API changes companion pull request [n/a]
• Public documentation issue/PR created,

Testing

Tested using big5 dataset, see #16837 (comment)

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.

[github-actions]

❌ Gradle check result for 0fafb49: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

[github-actions]

✅ Gradle check result for e1279da: SUCCESS

[github-actions]

✅ Gradle check result for 8ae7b14: SUCCESS

[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/OpenSearch/backport-2.x 2.x
# Navigate to the new working tree
pushd ../.worktrees/OpenSearch/backport-2.x
# Create a new branch
git switch --create backport/backport-17312-to-2.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 e3a6ccadc942c64e83bd224031bc4d1c6ab14623
# Push it to GitHub
git push --set-upstream origin backport/backport-17312-to-2.x
# Go back to the original working tree
popd
# Delete the working tree
git worktree remove ../.worktrees/OpenSearch/backport-2.x

Then, create a pull request where the base branch is 2.x and the compare/head branch is backport/backport-17312-to-2.x.