Feature: Add support for SelectTree without relationship using ->query()

[stefket]

This PR introduces the ability to use the SelectTree component without requiring an Eloquent relationship.

Previously, the component only worked when bound to a model relationship via ->relationship(...). However, there are valid use cases where no relationship exists — for example, when selecting navigation points to insert links inside a RichText editor.

To support this, a new ->query(...) method has been added. This allows developers to provide a custom query directly, enabling the SelectTree component to be used more flexibly across different scenarios.

Key changes:

• Added ->query() method as an alternative to ->relationship(...).
• Ensures that the component can still be used in contexts where no model relationship is defined.
• Keeps backward compatibility with existing ->relationship(...) usage.

Example usage:

SelectTree::make('category_id')
    ->query(fn() => Category::query(), 'name', 'parent_id')

This enhancement makes SelectTree more versatile and applicable beyond relationship-driven use cases.

[CodeWithDennis]

This is cool! I will try to find some time and spin up a new project making sure nothing breaks.

[gp-lnuff]

This would be a very welcome addition, as a workaround I've been using self-referencing relationships with target "group" records and scoping them out of my resources.

[CodeWithDennis]

Thanks!

[stefket]

Thanks for merging! :-)