PoC for UDFs

[asfimport]

The idea is to do a proof of concept before developing the UDF API or required kernels as a PR. 

This PoC will be looking into a few ideas. 

• Using Project (ProjectNodeOptions) to execute a simple Python function which serves as a UDF
• Using Aggregate (AggregateNodeOptions) to execute a simple Python function which servers as a UDF

Reporter: Vibhatha Lakmal Abeykoon / @vibhatha

_{Note: This issue was originally created as ARROW-15636. Please see the migration documentation for further details.}

[asfimport]

Vibhatha Lakmal Abeykoon / @vibhatha:
Note: This is not supposed to be a mergable PR, but just for the evaluation and brainstorming to identify limitations and required tools to designing UDFs. 

[asfimport]

Vibhatha Lakmal Abeykoon / @vibhatha:
In this task, the objective is to evaluate the existing API and limitations for the UDF design. 
A few tasks which are mainly focused; 

• How to use the existing function API and registry to register UDFs
• Evaluate the usage of ProjectNode and AggregateNode to provide UDFs 
• Finalize the API and initial design for UDFs. 

[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.