[Feature][3.5][Ready] Select2 grouped

[tabacitu]

This field allows you to specify a second entity, by which your select2 entries will be grouped.

Definition:

        $this->crud->addField([
            'label' => 'Articles grouped by categories',
            'type' => 'select2_grouped', //https://github.com/Laravel-Backpack/CRUD/issues/502
            'name' => 'article_id',
            'entity' => 'article',
            'attribute' => 'title',
            'group_by' => 'category', // the relationship to entity you want to use for grouping
            'group_by_attribute' => 'name', // the attribute on related model, that you want shown
            'group_by_relationship_back' => 'articles', // relationship from related model back to this model
        ]);

Screenshot: