fix(app-next): fix app-next dynamic plugin loading (#3182)

This change fixes the app-next ability to load frontend dynamic plugins
properly by ensuring the EXPERIMENTAL_MODULE_FEDERATION environment
variable is set to "true" when the package is built.

Signed-off-by: Stan Lewis <[email protected]>

Author: gashcrumb

packages/app-next/package.json

@@ -16,7 +16,7 @@
     "dist"
   ],
   "scripts": {
-    "build": "backstage-cli package build",
+    "build": "EXPERIMENTAL_MODULE_FEDERATION=true backstage-cli package build",
     "clean": "backstage-cli package clean",
     "lint": "backstage-cli package lint",
     "start": "backstage-cli package start --config ../../app-config.yaml",