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
Map.of(),
                    new Profile.VersionControl(0, 0)
                )
            );
            return null;
        }).when(service).createNewProfile(any(), any(), anyActionListener());
        
        Authentication.RealmRef realmRef1 = AuthenticationTestHelper.randomRealmRef(false);
        if (randomBoolean()) {
            realmRef1 = new Authentication.RealmRef(
                realmRef1.getName(),
                realmRef1.getType(),
                realmRef1.getNodeName(),
                new RealmDomain("hash", Set.of(new RealmConfig.RealmIdentifier(realmRef1.getType(), realmRef1.getName())))
            );
        }
        final Authentication authentication1 = AuthenticationTestHelper.builder().realm().realmRef(realmRef1).build();
        final Subject subject1 = authentication1.getEffectiveSubject();
        final PlainActionFuture<Profile> future1 = new PlainActionFuture<>();
        service.activateProfile(authentication1, future1);
        final Profile profile1 = future1.actionGet();
        assertThat(
            profile1.uid(),
            equalTo(
                "u_"
                    + Base64.getUrlEncoder()
                        .withoutPadding()
                        .encodeToString(MessageDigests.digest(new BytesArray(subject1.getUser().principal()), MessageDigests.sha256()))
                    + "_0"
            )