ino-nav-item: add support for sub items

[janivo]

Description

The current implementation of ino-nav-item lacks native support for sub-items, limiting its usability in scenarios that require hierarchical navigation structures. This ticket proposes enhancing the ino-nav-item component to include built-in support for sub-items, providing a more versatile solution for navigation.

Acceptance Criteria

• [ ] ino-nav-item includes native support for sub-items.
• [ ] Sub-items are visually distinguishable from parent items.
• [ ] Sub-items can be collapsed or expanded based on user interaction.
• [ ] Thoroughly test sub-item functionality in various use cases.

Example