Use feature-gates command line for kube-proxy

Avoid throwing `featureGates:` into the kube-proxy yaml, since it's
not in the right format. It should be

```
    featureGates:
      AllAlpha: true
```

Since FEATURES_GATES is set to `AllAlpha=true`, we can't just throw that
into the yaml file. Just pass along FEATURES_GATES in the command line
instead just like we do for all other services

hack/local-up-cluster.sh

@@ -817,13 +817,13 @@ kind: KubeProxyConfiguration
 clientConnection:
   kubeconfig: ${CERT_DIR}/kube-proxy.kubeconfig
 hostnameOverride: ${HOSTNAME_OVERRIDE}
-featureGates: ${FEATURE_GATES}
 mode: ${KUBE_PROXY_MODE}
 EOF
 
     sudo "${GO_OUT}/hyperkube" proxy \
       --config=/tmp/kube-proxy.yaml \
       --master="https://${API_HOST}:${API_SECURE_PORT}" >"${PROXY_LOG}" \
+      --feature-gates="${FEATURE_GATES}" \
       --v=${LOG_LEVEL} 2>&1 &
     PROXY_PID=$!