Fix API comment for the FailIndex Job pod failure policy action

Kubernetes-commit: 1395e2e02c50010e3043a61836ffb27cc4fe6842

Author: mimowo

batch/v1/types.go

@@ -124,6 +124,7 @@ const (
 	// This is an action which might be taken on a pod failure - mark the
 	// Job's index as failed to avoid restarts within this index. This action
 	// can only be used when backoffLimitPerIndex is set.
+	// This value is beta-level.
 	PodFailurePolicyActionFailIndex PodFailurePolicyAction = "FailIndex"
 
 	// This is an action which might be taken on a pod failure - the counter towards