[FEATURE] Add support for avatar stacked group element

[Defkon1]

Implement a BitAvatarGroup component inspired by the design and UX of the Bootstrap Italia Avatar Group List component.

Important

This component requires Dropdown component

Requirements:

Describe the list of requirements this feature needs:

• Create a reusable BitAvatarStackedGroup component following Bootstrap Italia's guidelines (docs).
• Support groups with textual, images and link avatar
• Support color variants (primary, secondary, success, danger, warning, info, light, dark, etc.).
• Support small and medium avatar sizes
• Responsive design and mobile-friendly behavior.
• Requires [FEATURE] Add avatar component #46

Acceptance Criteria:

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

References

• Bootstrap Italia - List of Avatars documentation (docs)

[albx]

@Defkon1 I removed from 0.2.3 milestone. I misunderstood the requirement, my bad.
The dropdown component up to now is not planned in the roadmap. I'll open an issue about it ASAP and then we could put both this issue and the dropdown one in a milestone.