Add API server config API v1alpha1

The `v1alpha1` API is not the *latest* version but it contains some new
structures not seen in `v1beta1` or `v1`.

Author: tengqm

content/en/docs/concepts/cluster-administration/system-traces.md

@@ -57,6 +57,9 @@ kind: TracingConfiguration
 samplingRatePerMillion: 100
 ```
 
+For more information about the `TracingConfiguration` struct, see
+[API server config API (v1alpha1)](/docs/reference/config-api/apiserver-config.v1alpha1/#apiserver-k8s-io-v1alpha1-TracingConfiguration).
+
 ## Stability
 
 Tracing instrumentation is still under active development, and may change in a variety of ways. This includes span names, attached attributes, instrumented endpoints, etc. Until this feature graduates to stable, there are no guarantees of backwards compatibility for tracing instrumentation.

content/en/docs/reference/_index.md

@@ -71,6 +71,7 @@ configure  kubernetes components or tools. Most of these APIs are not exposed
 by the API server in a RESTful way though they are essential for a user or an
 operator to use or manage a cluster.
 
+* [kube-apiserver configuration (v1alpha1)](/docs/reference/config-api/apiserver-config.v1alpha1/)
 * [kubelet configuration (v1beta1)](/docs/reference/config-api/kubelet-config.v1beta1/)
 * [kube-scheduler configuration (v1beta1)](/docs/reference/config-api/kube-scheduler-config.v1beta1/)
 * [kube-scheduler configuration (v1beta2)](/docs/reference/config-api/kube-scheduler-config.v1beta2/)