Update createDownloadResponseByReportVersion method to support COUNTER release 5.1

The createDownloadResponseByReportVersion method in the ReportExportHelper class needs to be updated to support COUNTER release 5.1 reports. Currently, the method only explicitly handles releases 4 and 5, returning XML for release 4 and JSON for release 5. As only release 4 uses a XML representation, we can modify this method to handle all releases other than 4 as JSON.

Acceptance Criteria:

1. The method should return JSON for all releases other than 4.

2. The method should return XML for release 4 reports.