[AI] Create design spec for AI TreeView AI

[mattrosno]

🔴 This work is being blocked until Developers are available to prioritize this work

Create a design spec for an AI version of TreeView, incorporating the AI label and aura gradient where appropriate. Design a solution for both light and dark themes.

[github-actions]

Thank you for submitting a feature request. Your proposal is open and will soon be triaged by the Carbon team.

If your proposal is accepted and the Carbon team has bandwidth they will take on the issue, or else request you or other volunteers from the community to work on this issue.

[mattrosno]

@aagonzales can you triage to make sure this enhancement should be done (accepted)?

[mattrosno]

Removing from the phase 2 milestone and closing as not planned for now. We can re-open if this gets prioritized in a future phase.