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(versionedDocument.toProfile(Set.of()));
                }, e -> {
                    if (ExceptionsHelper.unwrapCause(e) instanceof VersionConflictEngineException) {
                        
                        
                        getOrCreateProfileWithBackoff(subject, profileDocument, DEFAULT_BACKOFF.iterator(), listener);
                    } else {
                        listener.onFailure(e);
                    }
                }))
            )
        );
    }
    
    void getOrCreateProfileWithBackoff(
        Subject subject,
        ProfileDocument profileDocument,
        Iterator<TimeValue> backoff,
        ActionListener<Profile> listener
    ) {
        getVersionedDocument(profileDocument.uid(), ActionListener.wrap(versionedDocument -> {
            if (versionedDocument == null) {
                
                if (backoff.hasNext()) {
                    final TimeValue backoffTimeValue = backoff.next();
                    logger.debug("retrying get profile document [{}] after [{}] backoff", profileDocument.uid(), backoffTimeValue);
                    client.threadPool()
                        .schedule(
                            () -> getOrCreateProfileWithBackoff(subject, profileDocument, backoff, listener),
                            backoffTimeValue,