How are Item Definitions managed in Sitecore Commerce 9.1? They are referred to by the Composer, but that UI does not have an add function.
See: https://community.sitecore.net/technical_blogs/b/technical-marketing/posts/experience-commerce-entity-composer for an example of how they are used.
In the Composer, they are referenced here, but the associate UI does not allow creating new ones.
