Backport of #57870 to 7.x branch.
This change now also copies the op_type from the reindex request's destination index request to the actual index request being used in the bulk request.
For ensuring no document exists, the op_type create doesn't need to be copied, since Versions.MATCH_DELETED will copied from the 'mainRequest.getDestination().version()'.
The `version()` method on IndexRequest only returns Versions.MATCH_DELETED if op_type=create and no specific version has been specified.
However in order to be able to index into a data stream, the op_type must be create. So in order to support that the op_type must be copied from the reindex request's destination index request to the actual index request being used in the bulk request.
Relates to #53100 and #57788
c8031c6f99