Replace Paperclippable ContentConfig

The old Paperclip configuration was very clever and easy to use but it
was also a complicated implementation building on the complicated Spree
preference system.

I simplified this with Active Storage, storing simple references to blob
ids and default URLs as backup.

app/controllers/admin/contents_controller.rb

@@ -10,14 +10,14 @@ module Admin
 
     def update
       params.each do |name, value|
-        if ContentConfig.has_preference?(name) || ContentConfig.has_attachment?(name)
-          ContentConfig.public_send("#{name}=", value)
+        if value.is_a?(ActionDispatch::Http::UploadedFile)
+          blob = store_file(value)
+          update_preference("#{name}_blob_id", blob.id)
+        else
+          update_preference(name, value)
         end
       end
 
-      # Save any uploaded images
-      ContentConfig.save
-
       flash[:success] =
         t(:successfully_updated, resource: I18n.t('admin.contents.edit.your_content'))
 
@@ -26,6 +26,22 @@ module Admin
 
     private
 
+    def store_file(attachable)
+      ActiveStorage::Blob.create_and_upload!(
+        io: attachable.open,
+        filename: attachable.original_filename,
+        content_type: attachable.content_type,
+        service_name: :local,
+        identify: false,
+      )
+    end
+
+    def update_preference(name, value)
+      return unless ContentConfig.has_preference?(name)
+
+      ContentConfig.public_send("#{name}=", value)
+    end
+
     def preference_sections
       [
         PreferenceSections::HeaderSection.new,