Add partial aggregation pushdown support for Vertica

[vlad-lyutenko]

Description

Adding some aggregation pushdowns, except

• STDDEV and VARIANCE, because in case of situation when function can not be computed (like single value), Vertica returns NaN, but trino returns Null, so to be in line with trino we disable these types of pushdowns for now.
• avg pushdown for decimal values, because, when Vertica cast values to decimal value with some scale, instead of rounding, it just truncate it, but trino rounds values.

Additional context and related issues

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## Section
* Fix some things. ({issue}`issuenumber`)