Layout Assignment

### Technical TODO

For the first milestone, a simple layout assignment should be possible for category and product layout types. The assignment should happen from within the module itself, without interferring with current CMS layout assignment. If there is a corresponding assignment in Experience Studio, it just overrides any other old CMS assignment.

The implementation could be added to the top bar beside the save button. There could be a new "Assign" button which opens a modal with corresponding assignment selection.

Use entity select for both types(products/categories)