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.authz.store.DeprecationRoleDescriptorConsumer;
import org.elasticsearch.xpack.security.authz.store.FileRolesStore;
import org.elasticsearch.xpack.security.authz.store.NativePrivilegeStore;
import org.elasticsearch.xpack.security.authz.store.NativeRolesStore;
import org.elasticsearch.xpack.security.authz.store.RoleProviders;
import org.elasticsearch.xpack.security.ingest.SetSecurityUserProcessor;
import org.elasticsearch.xpack.security.operator.FileOperatorUsersStore;
import org.elasticsearch.xpack.security.operator.OperatorOnlyRegistry;
import org.elasticsearch.xpack.security.operator.OperatorPrivileges;
import org.elasticsearch.xpack.security.operator.OperatorPrivileges.OperatorPrivilegesService;
import org.elasticsearch.xpack.security.profile.ProfileService;
import org.elasticsearch.xpack.security.rest.SecurityRestFilter;
import org.elasticsearch.xpack.security.rest.action.RestAuthenticateAction;
import org.elasticsearch.xpack.security.rest.action.RestDelegatePkiAuthenticationAction;
import org.elasticsearch.xpack.security.rest.action.apikey.RestBulkUpdateApiKeyAction;
import org.elasticsearch.xpack.security.rest.action.apikey.RestClearApiKeyCacheAction;
import org.elasticsearch.xpack.security.rest.action.apikey.RestCreateApiKeyAction;
import org.elasticsearch.xpack.security.rest.action.apikey.RestGetApiKeyAction;
import org.elasticsearch.xpack.security.rest.action.apikey.RestGrantApiKeyAction;
import org.elasticsearch.xpack.security.rest.action.apikey.RestInvalidateApiKeyAction;
import org.elasticsearch.xpack.security.rest.action.apikey.RestQueryApiKeyAction;
import org.elasticsearch.xpack.security.rest.action.apikey.RestUpdateApiKeyAction;
import org.elasticsearch.xpack.security.rest.action.enrollment.RestKibanaEnrollAction;
import org.elasticsearch.xpack.security.rest.action.enrollment.RestNodeEnrollmentAction;
import org.elasticsearch.xpack.security.rest.action.oauth2.RestGetTokenAction;
import org.elasticsearch.xpack.security.rest.action.oauth2.RestInvalidateTokenAction;
import org.elasticsearch.xpack.security.rest.action.oidc.RestOpenIdConnectAuthenticateAction;
import org.elasticsearch.xpack.security.rest.action.oidc.RestOpenIdConnectLogoutAction;
import org.elasticsearch.xpack.security.rest.action.oidc.RestOpenIdConnectPrepareAuthenticationAction;
import org.elasticsearch.xpack.security.rest.action.privilege.RestClearPrivilegesCacheAction;