[pivot] add support for in Pivot on Druid (#3230)

superset/connectors/druid/models.py

@@ -817,6 +817,11 @@ class DruidDatasource(Model, BaseDatasource):
         """
         # TODO refactor into using a TBD Query object
         client = client or self.cluster.get_pydruid_client()
+
+        if DTTM_ALIAS in groupby:
+            groupby.remove(DTTM_ALIAS)
+            is_timeseries = True
+
         if not is_timeseries:
             granularity = 'all'
         inner_from_dttm = inner_from_dttm or from_dttm