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.rest.action.privilege.RestDeletePrivilegesAction;
import org.elasticsearch.xpack.security.rest.action.privilege.RestGetBuiltinPrivilegesAction;
import org.elasticsearch.xpack.security.rest.action.privilege.RestGetPrivilegesAction;
import org.elasticsearch.xpack.security.rest.action.privilege.RestPutPrivilegesAction;
import org.elasticsearch.xpack.security.rest.action.profile.RestActivateProfileAction;
import org.elasticsearch.xpack.security.rest.action.profile.RestDisableProfileAction;
import org.elasticsearch.xpack.security.rest.action.profile.RestEnableProfileAction;
import org.elasticsearch.xpack.security.rest.action.profile.RestGetProfilesAction;
import org.elasticsearch.xpack.security.rest.action.profile.RestSuggestProfilesAction;
import org.elasticsearch.xpack.security.rest.action.profile.RestUpdateProfileDataAction;
import org.elasticsearch.xpack.security.rest.action.realm.RestClearRealmCacheAction;
import org.elasticsearch.xpack.security.rest.action.role.RestClearRolesCacheAction;
import org.elasticsearch.xpack.security.rest.action.role.RestDeleteRoleAction;
import org.elasticsearch.xpack.security.rest.action.role.RestGetRolesAction;
import org.elasticsearch.xpack.security.rest.action.role.RestPutRoleAction;
import org.elasticsearch.xpack.security.rest.action.rolemapping.RestDeleteRoleMappingAction;
import org.elasticsearch.xpack.security.rest.action.rolemapping.RestGetRoleMappingsAction;
import org.elasticsearch.xpack.security.rest.action.rolemapping.RestPutRoleMappingAction;
import org.elasticsearch.xpack.security.rest.action.saml.RestSamlAuthenticateAction;
import org.elasticsearch.xpack.security.rest.action.saml.RestSamlCompleteLogoutAction;
import org.elasticsearch.xpack.security.rest.action.saml.RestSamlInvalidateSessionAction;
import org.elasticsearch.xpack.security.rest.action.saml.RestSamlLogoutAction;
import org.elasticsearch.xpack.security.rest.action.saml.RestSamlPrepareAuthenticationAction;
import org.elasticsearch.xpack.security.rest.action.saml.RestSamlSpMetadataAction;
import org.elasticsearch.xpack.security.rest.action.service.RestClearServiceAccountTokenStoreCacheAction;
import org.elasticsearch.xpack.security.rest.action.service.RestCreateServiceAccountTokenAction;
import org.elasticsearch.xpack.security.rest.action.service.RestDeleteServiceAccountTokenAction;
import org.elasticsearch.xpack.security.rest.action.service.RestGetServiceAccountAction;
import org.elasticsearch.xpack.security.rest.action.service.RestGetServiceAccountCredentialsAction;
import org.elasticsearch.xpack.security.rest.action.user.RestChangePasswordAction;