Add reason for attachdetach_controller_forced_detaches metric

Author: xing-yang

keps/sig-storage/2268-non-graceful-shutdown/README.md

@@ -411,8 +411,8 @@ Pick one more of these and delete the rest.
       - New metrics are added in Pod GC Controller:
         - `force_delete_pods_total{reason="out-of-service|terminated|orphaned|unscheduled"}`, the number of pods that are being forcefully deleted since the Pod GC Controller started.
         - `force_delete_pod_errors_total{reason="out-of-service|terminated|orphaned|unscheduled"}`, the number of errors encountered when forcefully deleting the pods since the Pod GC Controller started.
-      - For Attach Detach Controller, there's already a metric:
-        - `attachdetach_controller_forced_detaches`, the number of times the Attach Detach Controller performed a forced detach.
+      - For Attach Detach Controller, the following metric will be recorded if a force detach is performed because the node has the `out-of-service` taint or a timeout happens:
+        - `attachdetach_controller_forced_detaches{reason="out-of-service|timeout"}`, the number of times the Attach Detach Controller performed a forced detach.
       - There is also a `kube_node_spec_taint` in [kube-state-metrics](https://github.com/kubernetes/kube-state-metrics/blob/main/docs/node-metrics.md) that is a metric for the taint of a Kubernetes cluster node.
     - [Optional] Aggregation method:
     - Components exposing the metric: kube-controller-manager