Rename 'secret_key' to 'secret' in storage config (#28075)

Fix: Correct field name for r2 storage_config in realtimekit

- The secret_key field throws error "storage_config.secret_key" is not allowed
- The correct field name is secret

Author: svdf-org

src/content/docs/realtime/realtimekit/recording-guide/custom-cloud-storage.mdx

@@ -60,7 +60,7 @@ curl --request POST \
   "storage_config": {
     "type": "cloudflare",
     "access_key": "your-access-key",
-    "secret_key": "your-secret-key",
+    "secret": "your-secret-key",
     "bucket": "your-bucket-name",
     "path": "/"
   }