[Feedback] cluster graph command

Please leave feedback for the glab cluster graph command in this issue.

Please see the planned work in this epic: Kubernetes Dashboard Tree View (&13963). The graph API backend was built mainly for the dashboard, but we've also built this cli command to exercise the API.

Planned features for the cli command:

• Allow namespace filtering.
• Allow roots filtering once backend API supports it.
• ...

Latest demo: https://www.youtube.com/watch?v=xoxgenHb53M