Add partial Top-N pushdown support for Vertica

[vlad-lyutenko]

Description

Vertica doesn't have concept of NULLS FIRST/LAST for ORDER BY queries,
according to documentation:

NULL values are either first or last in the sort order, depending on data type:
INTEGER, INT, DATE/TIME: NULL has the smallest value.

FLOAT, BOOLEAN, CHAR, VARCHAR, ARRAY, SET: NULL has the largest value

So in case if trino hints to null ordering consistent with above rule we can do push down.

But if user for example has relaxed requirements for NULL's values or even know exactly that data is NULL free,
he could tweak the query to perform push down by making it consistent with Trino

for example by providing for

• int, date/time columns - always ASC with NULLS_FIRST and DESC with NULLS_LAST
• varchar/char/real columns - always ASC with NULLS_LAST and DESC with NULLS_FIRST

In this case pushdown will always happen.

Additional context and related issues

Release notes

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## Vertica connector
* Add support for partial Top-N pushdown. ({issue}`24217`)

[mosabua]

Can you add a Performance section like in the PostgreSQL connector docs to the Vertica doc .. and for now just have the Top-N pushdown link.. and then over time we add more and more...