fix: make EnsembleByKey transformSchema match output

core/src/main/python/synapse/ml/stages/EnsembleByKey.py

@@ -0,0 +1,13 @@
+# Copyright (C) Microsoft Corporation. All rights reserved.
+# Licensed under the MIT License. See LICENSE in project root for information.
+
+from pyspark.ml.common import inherit_doc
+from synapse.ml.stages._EnsembleByKey import _EnsembleByKey
+
+
+@inherit_doc
+class EnsembleByKey(_EnsembleByKey):
+    def getColNames(self):
+        if self.isSet(self.colNames):
+            return self.getOrDefault(self.colNames)
+        return [f"{self.getStrategy()}({name})" for name in self.getCols()]