Added Documents for kubernetes.io/enforce-mountable-secrets. (#31864)

* Added Documents for kubernetes.io/enforce-mountable-secrets.

* Modified the enforce-mountable-secrets docs.

Author: Shubham82

content/en/docs/reference/labels-annotations-taints.md

@@ -80,6 +80,14 @@ Used on: All Objects
 
 This annotation is used for describing specific behaviour of given object.
 
+## kubernetes.io/enforce-mountable-secrets {#enforce-mountable-secrets}
+
+Example: `kubernetes.io/enforce-mountable-secrets: "true"`
+
+Used on: ServiceAccount
+
+The value for this annotation must be **true** to take effect. This annotation indicates that pods running as this service account may only reference Secret API objects specified in the service account's `secrets` field.
+
 ## controller.kubernetes.io/pod-deletion-cost {#pod-deletion-cost}
 
 Example: `controller.kubernetes.io/pod-deletion-cost=10`