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
new ActionHandler<>(UpdateApiKeyAction.INSTANCE, TransportUpdateApiKeyAction.class),
            new ActionHandler<>(BulkUpdateApiKeyAction.INSTANCE, TransportBulkUpdateApiKeyAction.class),
            new ActionHandler<>(DelegatePkiAuthenticationAction.INSTANCE, TransportDelegatePkiAuthenticationAction.class),
            new ActionHandler<>(CreateServiceAccountTokenAction.INSTANCE, TransportCreateServiceAccountTokenAction.class),
            new ActionHandler<>(DeleteServiceAccountTokenAction.INSTANCE, TransportDeleteServiceAccountTokenAction.class),
            new ActionHandler<>(GetServiceAccountCredentialsAction.INSTANCE, TransportGetServiceAccountCredentialsAction.class),
            new ActionHandler<>(GetServiceAccountNodesCredentialsAction.INSTANCE, TransportGetServiceAccountNodesCredentialsAction.class),
            new ActionHandler<>(GetServiceAccountAction.INSTANCE, TransportGetServiceAccountAction.class),
            new ActionHandler<>(KibanaEnrollmentAction.INSTANCE, TransportKibanaEnrollmentAction.class),
            new ActionHandler<>(NodeEnrollmentAction.INSTANCE, TransportNodeEnrollmentAction.class),
            new ActionHandler<>(ProfileHasPrivilegesAction.INSTANCE, TransportProfileHasPrivilegesAction.class),
            new ActionHandler<>(GetProfilesAction.INSTANCE, TransportGetProfilesAction.class),
            new ActionHandler<>(ActivateProfileAction.INSTANCE, TransportActivateProfileAction.class),
            new ActionHandler<>(UpdateProfileDataAction.INSTANCE, TransportUpdateProfileDataAction.class),
            new ActionHandler<>(SuggestProfilesAction.INSTANCE, TransportSuggestProfilesAction.class),
            new ActionHandler<>(SetProfileEnabledAction.INSTANCE, TransportSetProfileEnabledAction.class),
            usageAction,
            infoAction
        );
    }
    @Override
    public List<ActionFilter> getActionFilters() {
        if (enabled == false) {
            return emptyList();
        }
        return singletonList(securityActionFilter.get());
    }
    @Override
    public List<RestHandler> getRestHandlers(
        Settings settings,