docs: fix redirect to WIP page (#12594)

Fixes the path for the temporary redirect for all /reference/api/group/*
routes to a new "Under
Development" page while the API is being built.

(cherry picked from commit 632a519680)

apps/docs/redirects.json

@@ -3260,8 +3260,8 @@
     "permanent": true
   },
   {
-    "source": "/api/group/:path*",
+    "source": "/reference/api/group/:path*",
     "destination": "/api-under-development",
     "permanent": false
   }
-]
+]