Enable pushdown of a few aggregation functions for ClickHouse Connector

[sylph-eu]

Description

Partially addresses #7100.

This PR enables a pushdown of the following aggregation functions: COUNT(DISTINCT) (except varchars), COVARIANCE, and CORRELATION.

Implementation of the rest of the functions have certain nuances that require additional efforts:

• Decimal implementation truncates digits outside of the scale, while Trino rounds them up.
• Statistical functions return NaN values on empty sets, while Trino expects NULL.

I'll have a look whether limitations above can be workarounded to improve pushdown "coverage".

Additional context and related issues

Continuous work on #7100.

Release notes

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# Section
* Pushdown more aggregation functions for ClickHouse connector. ({https://github.com/trinodb/trino/issues/7100}`7100`)