How to: $lttb(buckets_number, [field1, ... fieldN], x_field, y_field) - allow show down-sampled time series which will contains more outliers than avg or other kind of aggregation
If bucket_number is `auto`, then it will calculated as `toUInt64( ($to-$from) / $interval )`
Example usage:

```sql
$lttb(auto, category, event_time, count(*) c)
FROM requests GROUP BY category
```

Query will be transformed into:

```sql
SELECT category, lttb_result.1 AS event_time, lttb_result.2 AS c FROM (
    SELECT category, untuple(arrayJoin(lttb(toUInt64( ($to - $from) / $interval ))(event_time, cont(*) AS c))) AS lttb_result
    FROM requests WHERE $timeFilter GROUP BY category
) ORDER BY event_time
```

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