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/SecurityUsageTransportAction.java
import org.elasticsearch.common.util.concurrent.CountDown;
import org.elasticsearch.core.Nullable;
import org.elasticsearch.license.XPackLicenseState;
import org.elasticsearch.protocol.xpack.XPackUsageRequest;
import org.elasticsearch.tasks.Task;
import org.elasticsearch.threadpool.ThreadPool;
import org.elasticsearch.transport.TransportService;
import org.elasticsearch.xpack.core.XPackSettings;
import org.elasticsearch.xpack.core.action.XPackUsageFeatureAction;
import org.elasticsearch.xpack.core.action.XPackUsageFeatureResponse;
import org.elasticsearch.xpack.core.action.XPackUsageFeatureTransportAction;
import org.elasticsearch.xpack.core.security.SecurityFeatureSetUsage;
import org.elasticsearch.xpack.core.security.user.AnonymousUser;
import org.elasticsearch.xpack.security.audit.logfile.LoggingAuditTrail;
import org.elasticsearch.xpack.security.authc.Realms;
import org.elasticsearch.xpack.security.authc.support.mapper.NativeRoleMappingStore;
import org.elasticsearch.xpack.security.authz.store.CompositeRolesStore;
import org.elasticsearch.xpack.security.operator.OperatorPrivileges;
import org.elasticsearch.xpack.security.transport.filter.IPFilter;
import java.util.Arrays;
import java.util.Collections;
import java.util.Map;
import java.util.concurrent.atomic.AtomicReference;
import static java.util.Collections.singletonMap;
import static org.elasticsearch.xpack.core.XPackSettings.API_KEY_SERVICE_ENABLED_SETTING;
import static org.elasticsearch.xpack.core.XPackSettings.FIPS_MODE_ENABLED;
import static org.elasticsearch.xpack.core.XPackSettings.HTTP_SSL_ENABLED;
import static org.elasticsearch.xpack.core.XPackSettings.TOKEN_SERVICE_ENABLED_SETTING;
import static org.elasticsearch.xpack.core.XPackSettings.TRANSPORT_SSL_ENABLED;
public class SecurityUsageTransportAction extends XPackUsageFeatureTransportAction {