Fix aggregatorFactory meta merge exception

[es1220]

Fix HllSketch Metadata merge Exception

A segmentMetadata query with merge = true raises an exception because it does not implement the getMergingFactory method.

{
    "error": "Unknown exception",
    "errorMessage": "[io.druid.query.aggregation.datasketches.hll.HllSketchMergeAggregatorFactory] does not implement getMergingFactory(..)",
    "errorClass": "io.druid.java.util.common.UOE",
    "host": null
}