Agent modal inline validation was replaced with the generic hook

[Innagl]

Describe your changes

A reusable generic useFormValidation hook has been integrated into the "Add agent" modal, replacing the previous custom validation logic.

Write your issue number after "Fixes "

Fixes #3619

Please ensure all items are checked off before requesting a review:

• I deployed the code locally.
• I have performed a self-review of my code.
• I have included the issue # in the PR.
• I have labelled the PR correctly.
• The issue I am working on is assigned to me.
• I have avoided using hardcoded values to ensure scalability and maintain consistency across the application.
• I have ensured that font sizes, color choices, and other UI elements are referenced from the theme.
• My pull request is focused and addresses a single, specific feature.
• If there are UI changes, I have attached a screenshot or video to this PR.

[Br0wnHammer]

LGTM! 🚀