sql: support HAVING without GROUP BY clause

Allowed to make SELECT requests that have HAVING clause without
GROUP BY. It is possible when both - left and right parts of
request have aggregate function or constant value.

Closes #2364.

@TarantoolBot document
Title: HAVING without GROUP BY clause
A query with a having clause should also have a group by clause.
If you omit group by, all the rows not excluded by the where
clause return as a single group.
Because no grouping is performed between the where and having
clauses, they cannot act independently of each other. Having
acts like where because it affects the rows in a single group
rather than groups, except the having clause can still use
aggregates.
Having without group by is not supported for select from
multiple tables.

2011 SQL standard "Part 2: Foundation" 7.10 <having clause> p.381

Example:
SELECT MIN(s1) FROM te40 HAVING SUM(s1) > 0; -- is valid
SELECT 1 FROM te40 HAVING SUM(s1) > 0;       -- is valid
SELECT NULL FROM te40 HAVING SUM(s1) > 0;    -- is valid
SELECT date() FROM te40 HAVING SUM(s1) > 0;  -- is valid