[Task](ui): Add extra-small size to Button component

[MartinS-git]

Description

Add a new extra-small size variant to the Button component. This size is already defined in the Figma design system and is particularly useful in space-constrained contexts like the DataGrid toolbar, where actions like "Clear all" should have less visual weight and footprint.

Design Reference

Button Extra Small (all variants available: Primary, Default, Primary_Danger, Subdued):

Usage context – DataGrid Toolbar with filter pills and "Remove filters" button (extra-small):

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Phase 1: Button component

Add extra-small as a new size option to the Button component.

• Add "extra-small" to the ButtonSize type
• Define Tailwind classes for extra-small typography and padding (all variants)
• Update getButtonPadding, iconClasses, and Spinner size logic to handle the new size
• Add extra-small stories to Button.stories.tsx
• Update existing tests or add new tests for the extra-small size
• Verify visual alignment with Figma

Phase 2: DataGridToolbar usage

Use the new extra-small Button in the DataGridToolbar story as a real-world usage example.

• Update DataGridToolbar story "Complex Custom Layout": change the "Clear all" button to use size="extra-small"
• Update story description to mention the extra-small button usage