Add Filament Tree View plugin

[mashema]

This PR adds the Filament Tree View plugin to the plugin directory.

• Drag-and-drop tree view for Filament resources
• Drop-in replacement for Table with hierarchical data support
• Built on Laravel Adjacency List and Pragmatic Drag & Drop
• Supports Filament 4

Plugin: https://github.com/openplain/filament-tree-view
Packagist: https://packagist.org/packages/openplain/filament-tree-view

[github-actions]

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