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.profile.ActivateProfileAction;
import org.elasticsearch.xpack.core.security.action.profile.GetProfilesAction;
import org.elasticsearch.xpack.core.security.action.profile.SetProfileEnabledAction;
import org.elasticsearch.xpack.core.security.action.profile.SuggestProfilesAction;
import org.elasticsearch.xpack.core.security.action.profile.UpdateProfileDataAction;
import org.elasticsearch.xpack.core.security.action.realm.ClearRealmCacheAction;
import org.elasticsearch.xpack.core.security.action.role.ClearRolesCacheAction;
import org.elasticsearch.xpack.core.security.action.role.DeleteRoleAction;
import org.elasticsearch.xpack.core.security.action.role.GetRolesAction;
import org.elasticsearch.xpack.core.security.action.role.PutRoleAction;
import org.elasticsearch.xpack.core.security.action.rolemapping.DeleteRoleMappingAction;
import org.elasticsearch.xpack.core.security.action.rolemapping.GetRoleMappingsAction;
import org.elasticsearch.xpack.core.security.action.rolemapping.PutRoleMappingAction;
import org.elasticsearch.xpack.core.security.action.saml.SamlAuthenticateAction;
import org.elasticsearch.xpack.core.security.action.saml.SamlCompleteLogoutAction;
import org.elasticsearch.xpack.core.security.action.saml.SamlInvalidateSessionAction;
import org.elasticsearch.xpack.core.security.action.saml.SamlLogoutAction;
import org.elasticsearch.xpack.core.security.action.saml.SamlPrepareAuthenticationAction;
import org.elasticsearch.xpack.core.security.action.saml.SamlSpMetadataAction;
import org.elasticsearch.xpack.core.security.action.service.CreateServiceAccountTokenAction;
import org.elasticsearch.xpack.core.security.action.service.DeleteServiceAccountTokenAction;
import org.elasticsearch.xpack.core.security.action.service.GetServiceAccountAction;
import org.elasticsearch.xpack.core.security.action.service.GetServiceAccountCredentialsAction;
import org.elasticsearch.xpack.core.security.action.service.GetServiceAccountNodesCredentialsAction;
import org.elasticsearch.xpack.core.security.action.token.CreateTokenAction;
import org.elasticsearch.xpack.core.security.action.token.InvalidateTokenAction;
import org.elasticsearch.xpack.core.security.action.token.RefreshTokenAction;
import org.elasticsearch.xpack.core.security.action.user.AuthenticateAction;
import org.elasticsearch.xpack.core.security.action.user.ChangePasswordAction;
import org.elasticsearch.xpack.core.security.action.user.DeleteUserAction;