title: Attribute type single_selection with array_store needed
body: <p>I'm wondering why Shopware 5 is ignoring the array_store column for the attribute type single_selection. It seems that we need a complete mapped entity to these kind of attributes. But in this case I need a simple key/value pair. So, how to create a single_selection attribute on any attribute table with array_store's?</p>
  <p>In relation to the docs here, but not further explained for single_selection: <a href="https://developers.shopware.com/developers-guide/attribute-system/#define-own-single-and-multi-selection" rel="nofollow noreferrer">https://developers.shopware.com/developers-guide/attribute-system/#define-own-single-and-multi-selection</a></p>