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scrolling in ElasticSearch adapter


Hello,


I was thinking about adding [scrolling functionality](
https://www.elastic.co/guide/en/elasticsearch/reference/current/search-request-scroll.html)
to elastic search adapter. Since scrolling has non-negligible effect on the
cluster it should be selectively enabled on per query basis. So, likely,
user has to explicitly set "scroll flag" somewhere.

Most natural way seems in SQL. [Calcite sql grammar](
https://calcite.apache.org/docs/reference.html) has `SCROLL` keyword
(unused to my knowledge). There were also discussions about adding hints to
Calcite.

### Examples
```sql
-- special sql keyword ?
SCROLL select * from elastic;

-- assuming hints are available in calcite
/* HINT: scroll */ select * from elastic;
```

What people think about this use-case ? Are there better ideas ?

Regards,
Andrei.