[TASK] Add spacing between expandable items in Workspace Kind "Edit" form

[jenny-s51]

Certification

• I certify I am an Epic Owner for Kubeflow Notebooks 2.0 and expected to create planning-related issues.

Description

UX feedback per @tobiastal - there's no gap between expandable items.

PF theme:

MUI theme:

Acceptance Criteria

• Add 8px-16px spacing between expandable items in workspace kind form
• Spacing matches PatternFly design patterns for form layouts

[jenny-s51]

/area frontend
/area v2

[jenny-s51]

Closed via #737