Add KCP to glossary

reference: https://github.com/kubernetes-sigs/cluster-api/blob/main/CONTRIBUTING.md#contributors-ladder

docs/book/src/reference/glossary.md

@@ -172,6 +172,10 @@ A cluster that passes the Kubernetes conformance tests.
 
 Refers to the [main Kubernetes git repository](https://github.com/kubernetes/kubernetes) or the main Kubernetes project.
 
+### KCP
+
+Kubeadm Control plane Provider
+
 # L
 ---
 
@@ -314,4 +318,4 @@ A cluster created by a ClusterAPI controller, which is *not* a bootstrap cluster
 
 A collection of templates that define a set of worker nodes in the cluster. A ClusterClass contains zero or more WorkerClass definitions.
 
-See [ClusterClass](#clusterclass)
+See [ClusterClass](#clusterclass)