chore: lock the plugin boundary and remove 2.9.0 leftovers

plugins/vault/manifest.json

@@ -66,6 +66,14 @@
           }
         ]
       }
+    },
+    "http": {
+      "legacyRedirects": [
+        {
+          "from": "/vault/oidc/callback",
+          "to": "/oidc/callback"
+        }
+      ]
     }
   },
   "locales": "locales",