Align API documentation to behavior for REST API [process group/empty all connection requests]

https://github.com/apache/nifi/blob/main/nifi-nar-bundles/nifi-framework-bundle/nifi-framework/nifi-web/nifi-web-api/src/main/java/org/apache/nifi/web/api/ProcessGroupResource.java#L1639
 
POST /process-groups/{id}/empty-all-connections-requests
 
For this API, the documented response payload is of type ProcessGroupEntity.  It is actually of type DropRequestEntity.