feat: ordered-set aggregate in streaming queries

[stdrc]

Ordered-set aggregate functions are currently not supported in streaming queries. One of our user seems need this.

create materialized view mv as
select
  percentile_cont(0.5) within group (order by a),
  percentile_disc(0.5) within group (order by a)
from t;

[kwannoel]

Depends on #12570

[stdrc]

Depends on #12570

This is already merged. Are we currently doing Streaming Percentile or Streaming Approx Percentile? @kwannoel

[kwannoel]

Depends on #12570

This is already merged. Are we currently doing Streaming Percentile or Streaming Approx Percentile? @kwannoel

I'm working on Streaming Approx Percentile. Streaming Percentile is not worked on yet. You may take it up if interested.

[stdrc]

Since we already support approx_percentile, I guess it's not an urgent to support accurate percentile_cont/cont? We can remove the milestone for now.