ProcessingStage input validation fails when the input task is DocumentBatch and the data type is pyarrow

[ayushdg]

Describe the bug

The check in validate_input per stage:

        for attr in required_data_attrs:
            if not hasattr(task.data, attr):
                missing_data_attrs.append(attr)

w.r.t required attirs in the data object fails for pyarrow tables since columns don't pass this check

Steps/Code to reproduce bug

Please list minimal steps or code snippet for us to be able to reproduce the bug.

A helpful guide on on how to craft a minimal bug report http://matthewrocklin.com/blog/work/2018/02/28/minimal-bug-reports.

Expected behavior

A clear and concise description of what you expected to happen.

Additional context

Add any other context about the problem here.

[nightcityblade]

Hi, I'd like to work on this. I'll submit a PR shortly.

[nightcityblade]

I’m going to drop this for now. I was able to prototype a fix locally, but I couldn’t run the relevant project tests cleanly from my current non-Linux environment, so I don’t want to submit an unverified PR. Unclaiming so someone with the right setup can take it.