The Deployment controller was not propagating ReadyReplicas to underlying clusters causing these errors:
```
Error syncing cluster controller: Deployment.apps "federation-deployment" is invalid: status.availableReplicas: Invalid value: 5: cannot be greater than readyReplicas
```

This was caught in e2e testing and is a 1.6 regression for support that was added in #37959. Without this fix, users will be unable to scale up their deployments.