fix downsamplings output for normal N5 exports

Author: StephanPreibisch

src/main/java/net/preibisch/mvrecon/process/n5api/N5ApiTools.java

@@ -290,6 +290,8 @@ public static MultiResolutionLevelInfo[] setupMultiResolutionPyramid(
 					dataType,
 					compression );
 
+			driverVolumeWriter.setAttribute( datasetLevel, "downsamplingFactors", downsamplings[ level ] );
+
 			previousDim = dim;
 		}