Distinct command should respect the collation

--Collation parameter should be propagated to getExecutorDistinct().
--Collation parameter should be added to all LiteParsedQuerys in getExecutorDistinct().
--In the no-query case where we construct a solution consisting of just a DISTINCT_SCAN stage, ensure a fetch stage is added if there is a collation.
--In DistinctCommand::run(), the set of distinct elements should use collation-aware comparison.