ui: Make import_zone page a zone page to be able to delete it easily

ui/src/routes/domains/[dn]/import_zone/+page.ts

@@ -0,0 +1,10 @@
+import type { Load } from '@sveltejs/kit';
+
+export const load: Load = async({ parent }) => {
+    const data = await parent();
+
+    return {
+        ...data,
+        isZonePage: true,
+    }
+}