[CHORE] Argilla: remove pydantic warnings

[frascuchon]

Description

This PR removes some pydantic usage warnings, changing the class Config definition to the ConfigDict instance attribute.

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

(Please describe the tests that you ran to verify your changes. And ideally, reference tests)

• Test A
• Test B

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/)

[github-actions]

The URL of the deployed environment for this PR is https://argilla-quickstart-pr-5025-ki24f765kq-no.a.run.app