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
+ "] does not support auto-increment."
                )
            );
            return;
        }
        final int differentiator;
        try {
            differentiator = Integer.parseInt(differentiatorString);
        } catch (NumberFormatException e) {
            listener.onFailure(new ElasticsearchException("profile uid [{}] differentiator is not a number", e, uid));
            return;
        }
        
        if (differentiator >= DIFFERENTIATOR_UPPER_LIMIT) {
            listener.onFailure(
                new ElasticsearchException("profile differentiator value is too high for base Uid [{}]", uid.substring(0, index))
            );
            return;
        }
        
        final String newUid = baseUid + "_" + (differentiator + 1);
        createNewProfile(subject, newUid, listener);
    }
    private DomainConfig getDomainConfigForSubject(Subject subject) {
        final RealmDomain realmDomain = subject.getRealm().getDomain();
        if (realmDomain != null) {
            final DomainConfig domainConfig = domainConfigLookup.apply(realmDomain.name());
            if (domainConfig == null) {
                throw new ElasticsearchException(
                    "subject realm is under a domain [" + realmDomain.name() + "], but no associated domain config is found"