backend-next: add app-backend

Co-authored-by: Fredrik Adelöw <freben@gmail.com>
Co-authored-by: Johan Haals <johan.haals@gmail.com>
Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>

packages/backend-next/package.json

@@ -26,6 +26,7 @@
   },
   "dependencies": {
     "@backstage/backend-defaults": "workspace:^",
+    "@backstage/plugin-app-backend": "workspace:^",
     "@backstage/plugin-catalog-backend": "workspace:^",
     "@backstage/plugin-scaffolder-backend": "workspace:^"
   },