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.security.action.realm.TransportClearRealmCacheAction;
import org.elasticsearch.xpack.security.action.role.TransportClearRolesCacheAction;
import org.elasticsearch.xpack.security.action.role.TransportDeleteRoleAction;
import org.elasticsearch.xpack.security.action.role.TransportGetRolesAction;
import org.elasticsearch.xpack.security.action.role.TransportPutRoleAction;
import org.elasticsearch.xpack.security.action.rolemapping.TransportDeleteRoleMappingAction;
import org.elasticsearch.xpack.security.action.rolemapping.TransportGetRoleMappingsAction;
import org.elasticsearch.xpack.security.action.rolemapping.TransportPutRoleMappingAction;
import org.elasticsearch.xpack.security.action.saml.TransportSamlAuthenticateAction;
import org.elasticsearch.xpack.security.action.saml.TransportSamlCompleteLogoutAction;
import org.elasticsearch.xpack.security.action.saml.TransportSamlInvalidateSessionAction;
import org.elasticsearch.xpack.security.action.saml.TransportSamlLogoutAction;
import org.elasticsearch.xpack.security.action.saml.TransportSamlPrepareAuthenticationAction;
import org.elasticsearch.xpack.security.action.saml.TransportSamlSpMetadataAction;
import org.elasticsearch.xpack.security.action.service.TransportCreateServiceAccountTokenAction;
import org.elasticsearch.xpack.security.action.service.TransportDeleteServiceAccountTokenAction;
import org.elasticsearch.xpack.security.action.service.TransportGetServiceAccountAction;
import org.elasticsearch.xpack.security.action.service.TransportGetServiceAccountCredentialsAction;
import org.elasticsearch.xpack.security.action.service.TransportGetServiceAccountNodesCredentialsAction;
import org.elasticsearch.xpack.security.action.token.TransportCreateTokenAction;
import org.elasticsearch.xpack.security.action.token.TransportInvalidateTokenAction;
import org.elasticsearch.xpack.security.action.token.TransportRefreshTokenAction;
import org.elasticsearch.xpack.security.action.user.TransportAuthenticateAction;
import org.elasticsearch.xpack.security.action.user.TransportChangePasswordAction;
import org.elasticsearch.xpack.security.action.user.TransportDeleteUserAction;
import org.elasticsearch.xpack.security.action.user.TransportGetUserPrivilegesAction;
import org.elasticsearch.xpack.security.action.user.TransportGetUsersAction;
import org.elasticsearch.xpack.security.action.user.TransportHasPrivilegesAction;
import org.elasticsearch.xpack.security.action.user.TransportPutUserAction;
import org.elasticsearch.xpack.security.action.user.TransportSetEnabledAction;