Add test helpers for new backend system

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

packages/backend-test-utils/package.json

@@ -36,6 +36,8 @@
   },
   "dependencies": {
     "@backstage/backend-common": "^0.15.0-next.0",
+    "@backstage/backend-app-api": "^0.1.1-next.0",
+    "@backstage/backend-plugin-api": "^0.1.1-next.0",
     "@backstage/cli": "^0.18.1-next.0",
     "@backstage/config": "^1.0.1",
     "better-sqlite3": "^7.5.0",