Allow empty parent for new category

Choosing empty parent category will create a root taxon and a new
taxonomy record under the hood.

Author: chaimann

admin/app/components/solidus_admin/products/show/categories/new/component.html.erb

@@ -3,7 +3,7 @@
     <%= form_for @taxon, url: solidus_admin.product_taxons_path(@product), method: :post, html: { id: dom_id(@taxon) } do |f| %>
       <div class="flex flex-col gap-6 pb-4">
         <%= render component("ui/forms/field").text_field(f, :name, class: "required") %>
-        <%= render component("ui/forms/field").select(f, :parent_id, parent_taxon_options) %>
+        <%= render component("ui/forms/field").select(f, :parent_id, parent_taxon_options, include_blank: t(".none")) %>
         <%= render component("ui/forms/field").text_area(f, :description) %>
       </div>
     <% end %>

admin/app/components/solidus_admin/products/show/categories/new/component.yml

@@ -1,4 +1,5 @@
 en:
   cancel: "Cancel"
+  none: "None"
   submit: "Add Category"
   title: "New Category"