Native distinct counts in ClickHouse dialect

**Is your feature request related to a problem? Please describe.**
ClickHouse supports a number of functions to count distinct values: [uniq](https://clickhouse.tech/docs/en/sql-reference/aggregate-functions/reference/uniq/), uniqExact, [uniqHLL12](https://clickhouse.tech/docs/en/sql-reference/aggregate-functions/reference/uniqhll12/#agg_function-uniqhll12). However, they are not used in [ClickHouseQuery](https://github.com/cube-js/cube.js/blob/master/packages/cubejs-schema-compiler/src/adapter/ClickHouseQuery.js) 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**
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**Additional context**
Without this feature, `countDistinctApprox` is not supported at all, and — I think — `countDistinct` works slower than it could.