Render entity label as link if available

Closes #3482215

config/schema/inline_entity_form.schema.yml

@@ -54,6 +54,9 @@ field.widget.settings.inline_entity_form_complex:
     label_plural:
       type: label
       label: "Label (plural)"
+    label_link:
+      type: boolean
+      label: "Show label as link for existing entities"
     allow_new:
       type: boolean
       label: "Allow new"