Hll out of memory error

I got this error with hll query.

```
SET citus.count_distinct_error_rate to 0.01;

select data_info ->> 'domain', count(distinct userid)
from users
group by data_info ->> 'domain'
order by 2 desc;

ERROR: out of memory
DETAIL: Failed on request of size 131120 in memory context "multiset".
SQL state: 53200
```

Setting hll.force_groupagg to "on" and then the problem was resolved.

But group aggregation slower than count(distinct xxx) query. (3 times slower)

Is it possible to add memory setting options for hash aggregation?

@byucesoy