feat: add training task for qna

[davidberenstein1957]

Description

I added a TrainingTask.for_question_answering.

#3320

Type of change

(Please delete options that are not relevant. Remember to title the PR according to the type of change)

• New feature (non-breaking change which adds functionality)
• Refactor (change restructuring the codebase without changing functionality)
• Improvement (change adding some improvement to an existing functionality)

How Has This Been Tested

tests/integration/client/feedback/training/test_trainer.py

Checklist

• I added relevant documentation
• I followed the style guidelines of this project
• I did a self-review of my code
• I made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• I filled out the contributor form (see text above)
• I have added relevant notes to the CHANGELOG.md file (See https://keepachangelog.com/)

[tomaarsen]

@davidberenstein1957 Great stuff, a few comments here and there, but I think this is looking good

[github-actions]

The URL of the deployed environment for this PR is https://argilla-quickstart-pr-3740-ki24f765kq-no.a.run.app

[codecov]

Codecov Report

Patch has no changes to coverable lines.

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