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/profile/ProfileService.java
listener.onResponse(resultsAndErrors.results().iterator().next().v2());
            } else if (resultsAndErrors.errors().size() == 1) {
                final Exception exception = resultsAndErrors.errors().values().iterator().next();
                logger.error(exception.getMessage());
                listener.onFailure(exception);
            } else {
                assert false : "a single subject must have either a single result or error";
                listener.onFailure(new ElasticsearchException("a single subject must have either a single result or error"));
            }
        }, listener::onFailure));
    }
    private void searchVersionedDocumentsForSubjects(
        List<Subject> subjects,
        ActionListener<SubjectSearchResultsAndErrors<VersionedDocument>> listener
    ) {
        if (subjects.isEmpty()) {
            listener.onResponse(new SubjectSearchResultsAndErrors<>(List.of(), Map.of()));
            return;
        }
        tryFreezeAndCheckIndex(listener).ifPresent(frozenProfileIndex -> {
            frozenProfileIndex.checkIndexVersionThenExecute(listener::onFailure, () -> {
                final MultiSearchRequest multiSearchRequest = new MultiSearchRequest();
                subjects.forEach(subject -> multiSearchRequest.add(buildSearchRequestForSubject(subject)));
                executeAsyncWithOrigin(
                    client,
                    getActionOrigin(),
                    MultiSearchAction.INSTANCE,
                    multiSearchRequest,
                    ActionListener.wrap(
                        multiSearchResponse -> listener.onResponse(convertSubjectMultiSearchResponse(multiSearchResponse, subjects)),