Requires ARROW-12759.

We have a scalar aggregate kernel for this already and hopefully the implementation can be reused. Note, Pandas actually doesn't expose this in DataFrameGroupBy.

Reporter: David Li / @lidavidm

Related issues:

• [C++] Implement hash_aggregate kernels (umbrella issue) (is a child of)

_{Note: This issue was originally created as ARROW-13310. Please see the migration documentation for further details.}