Feature Request: inQuery_

Sometimes it is desirable to be able to take queries that return a list of values and be able to use them in an "in" clause.

Example:
```sql
SELECT col1, col2 FROM tbl1 WHERE tbl1.col3 IN
(SELECT DISTINCT col3 FROM tbl1 WHERE cond1 AND cond2 LIMIT n)
FOR UPDATE SKIP LOCKED
```

Currently, `in_` requires you to have a list of `QGenExpr`s, It would be nice if a query could be placed on the right side of an `in_` like combinator instead of a haskell list.

I was hoping `subselect_` could fulfill my desires here, but it seems to only to take one argument, so I can't tell if it can be used for the above.

Is this something that would be possible?