Better metrics for OpenSearch duplicate documents

[dlvenable]

Is your feature request related to a problem? Please describe.

We have had some difficulty adding up metrics when some events are duplicates. With the current metrics, we cannot tell how many documents were counted as duplicates in OpenSearch. This can result in being unable to add up the number of events in with the actual documents in OpenSearch.

Goal:

documentsSuccess - documentsDuplicates == count on OpenSearch

Describe the solution you'd like

Add a metrics for duplicate documents. To determine if a document is a duplicate, we can check _seq_no > 0. If this is true, then we can consider this document to be a duplicate.