[DOC] New cluster setting for dynamic pruning feature in cardinality aggregation

[bowenlan-amzn]

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Tell us about your request. Provide a summary of the request and all versions that are affected.

opensearch-project/OpenSearch#13821

New cluster setting that can dynamically tune the threshold of supported maximum cardinality for doing the pruning
search.dynamic_pruning.cardinality_aggregation_threshold
Set to 0 to disable the feature.

What other resources are available? Provide links to related issues, POCs, steps for testing, etc.

[bowenlan-amzn]

We will try to get this in 2.15, I will create a PR for documentation shortly.