[C++][Python] UDF Aggregate Function Implementation

[asfimport]

Here we will be implementing the UDF support for aggregate functions.

Reporter: Vibhatha Lakmal Abeykoon / @vibhatha
Assignee: Vibhatha Lakmal Abeykoon / @vibhatha

PRs and other links:

• GitHub Pull Request #14527

_{Note: This issue was originally created as ARROW-15641. Please see the migration documentation for further details.}

[asfimport]

Todd Farmer / @toddfarmer:
This issue was last updated over 90 days ago, which may be an indication it is no longer being actively worked. To better reflect the current state, the issue is being unassigned. Please feel free to re-take assignment of the issue if it is being actively worked, or if you plan to start that work soon.

[asfimport]

Apache Arrow JIRA Bot:
This issue was last updated over 90 days ago, which may be an indication it is no longer being actively worked. To better reflect the current state, the issue is being unassigned per project policy. Please feel free to re-take assignment of the issue if it is being actively worked, or if you plan to start that work soon.