[Feature Request] Support for _doc_count field in star tree to represent _doc_count as part of aggregations response

[bharath-techie]

Is your feature request related to a problem? Please describe

Any bucketized aggregation results have _doc_count as part of response. If the user has not added any _doc_count field to account for pre-aggregations, the default behavior is _doc_count will be incremented by 1 for each doc, and if the _doc_count value is provided , then OpenSearch uses the value directly.

Describe the solution you'd like

As part of star tree indexing flow, during flush , we will always add _doc_count field to the mapping. The identity value ( when no value is provided ) for each doc will be 1 and otherwise actual _doc_count value will be taken into account.

So as part of merge or query , there will always be _doc_count field present for each doc.

Related component

Indexing:Performance

Describe alternatives you've considered

No response

Additional context

No response