[FEATURE] Add BottomNav component

[albx]

Implement a reusable Razor component for Bottomnav, following the styles and guidelines in Bootstrap Italia - BottomNav. Support all documented features, such as active state, icons, and accessibility.

Requirements:

• Implement a Razor component (e.g., BitBottomNav.razor) encapsulating Bootstrap Italia BottomNav styles.
• Support for active state, icons, and label display.
• Expose parameters for ARIA/accessibility attributes and navigation items.
• Add XML documentation for all public parameters.

Acceptance Criteria:

• The component renders valid Bootstrap Italia Bottomnav markup.
• All documented variants and features are supported via parameters.
• The component is unit tested for major variants and behaviors.
• Usage examples are provided in the documentation or a sample page.

References:

• Bootstrap Italia - BottomNav Documentation