Route webhook to all replicas
This is something you'd have to build. Kubernetes doesn't natively offer this as a pattern.

There are a few approached you can take, but a common on is to use a queue that has this functionality. I'd suggest starting with Nats because it's a CNCF project that is easy to run natively in Kubernetes. When one of your replicas receives the request, it can post a message to the queue that can deliver the message to every subscriber.