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
if (User.isInternal(subject.getUser())) {
            listener.onFailure(
                new IllegalStateException("profile should not be created for internal user [" + subject.getUser().principal() + "]")
            );
            return;
        }
        searchVersionedDocumentForSubject(subject, ActionListener.wrap(versionedDocument -> {
            if (versionedDocument == null) {
                final DomainConfig domainConfig = getDomainConfigForSubject(subject);
                if (domainConfig == null || false == domainConfig.literalUsername()) {
                    assert domainConfig == null || domainConfig.suffix() == null;
                    
                    createNewProfile(subject, ProfileDocument.computeBaseUidForSubject(subject) + "_0", listener);
                } else {
                    assert domainConfig.suffix() != null;
                    validateUsername(subject);
                    createNewProfile(subject, "u_" + subject.getUser().principal() + "_" + domainConfig.suffix(), listener);
                }
            } else {
                updateProfileForActivate(subject, versionedDocument, listener);
            }
        }, listener::onFailure));
    }
    public void updateProfileData(UpdateProfileDataRequest request, ActionListener<AcknowledgedResponse> listener) {
        final XContentBuilder builder;
        try {
            builder = XContentFactory.jsonBuilder();
            builder.startObject();
            {
                builder.field("user_profile");