Implement a hash aggregate approximate quantile kernel. We have a scalar aggregate version of this (named tdigest) using t-digest.

Reporter: Ian Cook / @ianmcook
Assignee: David Li / @lidavidm

Related issues:

• [C++] Implement hash_aggregate kernels (umbrella issue) (is a child of)
• [C++] Implement hash_aggregate exact quantile kernel (relates to)
• [C++][Compute] Implement approximate quantile kernel (relates to)
• [C++] Add TDigest::Merge(const TDigest&) (is related to)
• [R] Binding for median() and quantile() aggregation functions (is depended upon by)

PRs and other links:

• GitHub Pull Request #10860

_{Note: This issue was originally created as ARROW-13520. Please see the migration documentation for further details.}