Support string functions like UPPER, LOWER, SUBSTRING in WHERE clause

String functions are supported in the SELECT and GROUP BY clauses but not in the WHERE one.

The exception being thrown is similar to the following:

LOWER while executing SQL: "
select lower(d.name), avg(f.my_measure)
from fact_table f
inner join dim_table d on f.fk_id = d.pk_id
where lower(d.name) = 'my_username'
group by lower(d.name)
LIMIT 50000"