fix(docs): control plane resources required label from v1.5.0

Signed-off-by: Dario Tranchitella <[email protected]>

docs/book/src/developer/providers/migrations/v1.4-to-v1.5.md

@@ -38,6 +38,8 @@ maintainers of providers and consumers of our Go API.
 - Introduced function `CollectInfrastructureLogs` at the `ClusterLogCollector` interface in `test/framework/cluster_proxy.go` to allow collecting infrastructure related logs during tests.
 - A `GetTypedConfigOwner` function has been added to the `sigs.k8s.io./cluster-api/bootstrap/util` package. It is equivalent to `GetConfigOwner` except that it uses the cached typed client instead of the uncached unstructured client, so `GetTypedConfigOwner` is expected to be more performant.
 - `ClusterToObjectsMapper` in `sigs.k8s.io./cluster-api/util` has been deprecated, please use `ClusterToTypedObjectsMapper` instead.
+- Control Plane providers objects, such as the Kubeconfig and Certificate Authority Secret resources, must be labelled with the key-value pair `cluster.x-k8s.io/cluster-name=${CLUSTER_NAME}`.
+  This is required for the CAPI managers caches to store and retrieve them for the required operations such as issuing a join token, and generating certificates.     
 
 ### Suggested changes for providers