Support for AggregateFunction data type

[srikanthccv]

This is a parent issue to add support for the data type AggregateFunction. Several different categories of quantile functions can be used with AggregateFunction. I think each of them deserves their own type as they have custom serialization/deserialization. I would like to help with this effort starting with quantile(s)DDSketch and quantileBFloat16 and more to follow. I have a quick prototype for DDSketch here main...srikanthccv:ch-go:ddsketch.

@ernado do you have anything in mind how the API should look like?

Tasks

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1. Add support for uniq AggregateFunction
2. Add support for anyIf AggregateFunction
3. Add support for quantiles AggregateFunction
4. Add support for quantilesDeterministic AggregateFunction
5. Add support for quantilesTiming(Weighted) AggregateFunction
6. Add support for quantilesExact(Weighted) AggregateFunction
7. Add support for quantilesTDigest AggregateFunction
8. Add support for quantilesBFloat16 AggregateFunction
9. Add support for quantilesDDSketch AggregateFunction

[srikanthccv]

The encode and decode parts should be fairly straightforward from the serialize and deserialize methods from ClickHouse. One thing that I am not sure what is the best way to go about it is ColumnType because it can vary a lot but that doesn't really matter at all because the underlying state decode and encode dictate everything.