Support conditional script update of documents in the OpenSearch sink

[graytaylor0]

Is your feature request related to a problem? Please describe.
As a user of the OpenSearch sink, I would like to conditionally update documents by comparing the existing document in OpenSearch with the updated document.

Describe the solution you'd like
An option to specify a script parameter that will apply to update and upsert operation in the sink (https://opensearch.org/docs/latest/api-reference/document-apis/update-document/#script-example).

This requires that the incoming update documents contain the fields that are referenced in the script.

Describe alternatives you've considered (Optional)
One alternative to having OpenSearch handle this would be to have Data Prepper handle it, which would mean an extra read of each document with an update or upsert operation, and then relying on Data Prepper expression as the condition instead of the script. the benefit of this approach would be that we could support comparisons on Data Prepper metadata, instead of requiring the data be in the Event.

Additional context
Add any other context or screenshots about the feature request here.