[FEATURE] Implement BitDropdown component

[albx]

Implement a BitDropdown component inspired by the design and UX of the Bootstrap Italia Dropdown component.

Requirements:

• Create a reusable BitDropdown component following Bootstrap Italia's guidelines (docs).
• Support for all dropdown variants as documented.
• Expose properties for menu items, icons, disabled/read-only state, and custom content.
• Allow customization of trigger (button, icon, etc.).
• Ensure accessibility and keyboard navigation according to Bootstrap Italia standards.
• Responsive design and mobile-friendly behavior.

Acceptance Criteria:

• The component renders valid Bootstrap Italia dropdown markup.
• All documented variants and features are supported via parameters.
• The component is unit tested for all major styles and behaviors.
• Usage examples are provided in the documentation or a sample page.
• Accessibility and keyboard navigation are fully implemented.

References

• Bootstrap Italia Dropdown Documentation: https://italia.github.io/bootstrap-italia/docs/componenti/dropdown/