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
);
        assertThat(profile1.user().username(), equalTo(subject1.getUser().principal()));
        
        Authentication.RealmRef realmRef2 = AuthenticationTestHelper.randomRealmRef(false);
        realmRef2 = new Authentication.RealmRef(
            realmRef2.getName(),
            realmRef2.getType(),
            realmRef2.getNodeName(),
            new RealmDomain("literal", Set.of(new RealmConfig.RealmIdentifier(realmRef2.getType(), realmRef2.getName())))
        );
        
        final User user2 = AuthenticationTestHelper.userWithRandomMetadataAndDetails(
            randomFrom(randomAlphaOfLengthBetween(3, 8), randomAlphaOfLengthBetween(1, 8) + "-" + randomAlphaOfLengthBetween(0, 8))
        );
        final Authentication authentication2 = AuthenticationTestHelper.builder().user(user2).realm().realmRef(realmRef2).build();
        final Subject subject2 = authentication2.getEffectiveSubject();
        final PlainActionFuture<Profile> future2 = new PlainActionFuture<>();
        service.activateProfile(authentication2, future2);
        final Profile profile2 = future2.actionGet();
        assertThat(profile2.uid(), equalTo("u_" + subject2.getUser().principal() + "_suffix"));
        assertThat(profile2.user().username(), equalTo(subject2.getUser().principal()));
        
        final List<Character> invalidFirstCharsOfLiteralUsername = VALID_NAME_CHARS.stream()
            .filter(c -> false == Character.isLetterOrDigit(c))
            .toList();
        final List<Character> invalidCharsOfLiteralUsername = invalidFirstCharsOfLiteralUsername.stream().filter(c -> c != '-').toList();
        final String invalidLiteralUsername = randomFrom(
            "",
            "fóóbár",
            randomAlphaOfLength(257),