As we are rolling out the user profile feature, we'd like to expand the [Usage API](https://www.elastic.co/guide/en/elasticsearch/reference/current/usage-api.html) to report usage stats of user profiles such as (1) number of enabled user profiles and (2) number of user profiles that are [activated](https://www.elastic.co/guide/en/elasticsearch/reference/current/security-api-activate-user-profile.html) over the past X days. 

Response of the Usage API already contains a `security` field that groups relevant stats from security related features. We expect the new stats for user profiles should be added under it as well, for example:
```
{
  "security: {
    "user_profile": {
      "activated": 78,
      "recently_activated": 42  <1>
    }
  }
}
```
<1> The use of `recently_` is chosen to avoid the field to be tied to a specific time period so it is easier to evolve the definition in future.

x-pack/plugin/security/src/main/java/org/elasticsearch/xpack/security/Security.java
import org.elasticsearch.xpack.core.security.action.user.GetUserPrivilegesAction;
import org.elasticsearch.xpack.core.security.action.user.GetUsersAction;
import org.elasticsearch.xpack.core.security.action.user.HasPrivilegesAction;
import org.elasticsearch.xpack.core.security.action.user.ProfileHasPrivilegesAction;
import org.elasticsearch.xpack.core.security.action.user.PutUserAction;
import org.elasticsearch.xpack.core.security.action.user.SetEnabledAction;
import org.elasticsearch.xpack.core.security.authc.AuthenticationFailureHandler;
import org.elasticsearch.xpack.core.security.authc.AuthenticationServiceField;
import org.elasticsearch.xpack.core.security.authc.DefaultAuthenticationFailureHandler;
import org.elasticsearch.xpack.core.security.authc.InternalRealmsSettings;
import org.elasticsearch.xpack.core.security.authc.Realm;
import org.elasticsearch.xpack.core.security.authc.RealmConfig;
import org.elasticsearch.xpack.core.security.authc.RealmSettings;
import org.elasticsearch.xpack.core.security.authc.jwt.JwtRealmsServiceSettings;
import org.elasticsearch.xpack.core.security.authc.support.UsernamePasswordToken;
import org.elasticsearch.xpack.core.security.authz.AuthorizationEngine;
import org.elasticsearch.xpack.core.security.authz.AuthorizationServiceField;
import org.elasticsearch.xpack.core.security.authz.RestrictedIndices;
import org.elasticsearch.xpack.core.security.authz.accesscontrol.DocumentSubsetBitsetCache;
import org.elasticsearch.xpack.core.security.authz.accesscontrol.IndicesAccessControl;
import org.elasticsearch.xpack.core.security.authz.accesscontrol.SecurityIndexReaderWrapper;
import org.elasticsearch.xpack.core.security.authz.permission.FieldPermissions;
import org.elasticsearch.xpack.core.security.authz.permission.FieldPermissionsCache;
import org.elasticsearch.xpack.core.security.authz.permission.SimpleRole;
import org.elasticsearch.xpack.core.security.authz.store.ReservedRolesStore;
import org.elasticsearch.xpack.core.security.authz.store.RoleRetrievalResult;
import org.elasticsearch.xpack.core.security.support.Automatons;
import org.elasticsearch.xpack.core.security.user.AnonymousUser;
import org.elasticsearch.xpack.core.ssl.SSLConfigurationSettings;
import org.elasticsearch.xpack.core.ssl.SSLService;