chore: Downgrade back to Apollo Server v4

The NestJS integration with v5 still has issues due
to the use of the deprecated playground

https://github.com/nestjs/graphql/pull/3669#issuecomment-3360861537

packages/harden-plugin/package.json

@@ -25,7 +25,7 @@
         "graphql-query-complexity": "^0.12.0"
     },
     "peerDependencies": {
-      "@apollo/server": "^5.0.0"
+      "@apollo/server": "^4.12.2"
     },
     "devDependencies": {
         "@vendure/common": "3.4.3",