Adding nullable menthod

Author: mzitnik

clickhouse-data/src/main/java/com/clickhouse/data/ClickHouseColumn.java

@@ -647,6 +647,10 @@ public static ClickHouseColumn of(ClickHouseDataType dataType, boolean nullable)
         return ClickHouseColumn.of("", dataType, nullable);
     }
 
+    public static ClickHouseColumn nullable(ClickHouseDataType dataType) {
+        return ClickHouseColumn.of(dataType, true);
+    }
+
     public static ClickHouseColumn string(boolean nullable) {
         return ClickHouseColumn.of(ClickHouseDataType.String, nullable);
     }