docs: removed outdated warning and enhanced tree component documentation

[laske185]

This pull request refines the documentation for the Tree component in docs/30-components/tree.mdx. The changes improve clarity, update the keyboard navigation guide, and enhance the description of the component's usage and functionality.

Documentation Improvements:

• Simplified Component Description: The description of the Tree component was rewritten for better readability and conciseness, removing the preview warning and emphasizing its hierarchical structure and expand/collapse functionality.
• Enhanced Usage Details: The usage section was updated to provide clearer examples of where the Tree component is applicable (e.g., navigation bars, file directories). It also specifies how attributes like _label, _href, _active, and _open are used.

Keyboard Navigation Updates:

• Revised Key Descriptions: The keyboard navigation guide was rewritten for improved clarity. It now uses clearer terminology, such as ↑ / ↓ for navigation within the same level and →/← for expanding/collapsing menus. Additional details include how alphanumeric keys can be used for quick navigation.

The A11y and PO reviews will only take place after all other DoD steps have been completed by the Developer:

• Meaningful pull request title for the release notes
• Pull request is linked to an issue and all changes relate to the issue
• Tests to protect this code implemented (if applicable)
• Manual test performed successfully (if applicable)
• Documentation or migration has been updated (if applicable)

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[laske185]

I have read the CLA Document and I hereby sign the CLA