Enable customisation of OpenAPI test API model powered by Scalar

[kashyapro]

Update the modal opened by "Test it" to make request setup faster and clearer.

Problem

The current modal makes it harder to:

• Scan required inputs
• Understand request structure
• Submit and inspect results quickly

Requirements

Layout & Structure

• Show required fields first
• Group inputs into clear sections
• Improve spacing, labels, and field hierarchy

Actions & Feedback

• Make the primary action more prominent
• Show request and response areas more clearly

Responsiveness

• Keep the modal usable on smaller screens

Acceptance Criteria

• Required fields are easy to identify at a glance
• Users can complete a test request without confusion
• Request input and response output are visually distinct
• The modal layout works well on desktop and laptop widths
• The primary submit action stays obvious throughout the flow