add support setting session params in query

[benMen87]

see TestSplitQueriesWithSession for syntax of setting session params inline - motivation is to enable easy sessions setting for specific query without making test suite too complex structure

example:

--SET SESSION join_reordering_strategy = 'NONE';
SELECT
  l_orderkey,
  l_partkey,
  l_suppkey,
  l_shipdate
FROM
  lineitem
WHERE
l_extendedprice <= 950;