Native distinct counts in ClickHouse dialect

[igorlukanin]

Is your feature request related to a problem? Please describe.
ClickHouse supports a number of functions to count distinct values: uniq, uniqExact, uniqHLL12. However, they are not used in ClickHouseQuery adapter to support countDistinctApprox and other types of aggregations.

Describe the solution you'd like
With the guidance of the Cube.js team and taking other adapters as examples, these functions should be used in the adapter.

Describe alternatives you've considered
—

Additional context
Without this feature, countDistinctApprox is not supported at all, and — I think — countDistinct works slower than it could.

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[bhardwajparth51]

@igorlukanin Hey is this open to work. I would love to be assigned