CV2-6653: Articles :: Add max length limitation to match UI validation

[melsawy]

Description

Add a validation to FactCheck and Explainer to verify the length for the article fields to match UI validation

• Add validations per field (title, url and description)
• Truncate fields for automation import (i.e user is a BotUser)

References: CV2-6653

How to test?

Added unit tests

Checklist

• I have performed a self-review of my code and ensured that it is safe and runnable, that code coverage has not decreased, and that there are no new Code Climate issues. I have also followed Meedan's internal coding guidelines.

[caiosba]

Reviewed in pair in our 1:1 ✔️

[melsawy]

@caiosba, I updated the PR to validate each field independently. I also added automatic truncation for these fields when the import is performed by a BotUser (automation import), rather than implementing truncation logic across all Zapier integrations.