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/test/java/org/elasticsearch/xpack/security/profile/ProfileServiceTests.java
}, threadPool)
        );
        doAnswer(invocation -> {
            @SuppressWarnings("unchecked")
            final var listener = (ActionListener<ProfileService.VersionedDocument>) invocation.getArguments()[1];
            listener.onResponse(null);
            return null;
        }).when(service).searchVersionedDocumentForSubject(any(), anyActionListener());
        doAnswer(invocation -> {
            final Object[] arguments = invocation.getArguments();
            final Subject subject = (Subject) arguments[0];
            final User user = subject.getUser();
            final Authentication.RealmRef realmRef = subject.getRealm();
            final String uid = (String) arguments[1];
            @SuppressWarnings("unchecked")
            final var listener = (ActionListener<Profile>) arguments[2];
            listener.onResponse(
                new Profile(
                    uid,
                    true,
                    0,
                    new Profile.ProfileUser(
                        user.principal(),
                        Arrays.asList(user.roles()),
                        realmRef.getName(),
                        realmRef.getDomain() == null ? null : realmRef.getDomain().name(),
                        user.email(),
                        user.fullName()
                    ),
                    Map.of(),