Support AggregateFunction type

[srikanthccv]

I have a use case where I want to write the quantile sketch serialized data that is compatible with the ClickHouse server. For example, quantileBFloat16 uses a hash of bfloat16 using Data = HashMapWithStackMemory<BFloat16, Weight, TrivialHash, 4>;. It would be very helpful to send the go type map[uint16]uint64. In this PR we add the DDSketch ClickHouse/ClickHouse#56342, which has its own binary representation. The sketches data from systems could come pre-aggregated that can be combined on the ClickHouse server to produce the quantile at the query time by merging them.

I would like to work on add support for AggregateFunction and AggregateFunction(quantilesDDSketch ...)) to begin with. I see the go client library internally uses https://github.com/ClickHouse/ch-go. Let me know what you think.

[iyuroch]

Are there any plans to add this functionality?

[jkaflik]

This enhancement was requested in #1292.

@srikanthccv any contributions are welcomed!

[roshaans]

Does the client not support even basic Aggregation Function Types like Count?

decode error: clickhouse: unsupported column type "AggregateFunction(count)"