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
client,
            profileIndex,
            mock(ClusterService.class),
            domainName -> new DomainConfig(domainName, Set.of(), true, "suffix"),
            threadPool
        );
        final PlainActionFuture<Profile> future = new PlainActionFuture<>();
        service.maybeIncrementDifferentiatorAndCreateNewProfile(
            subject,
            ProfileDocument.fromSubjectWithUid(subject, "u_" + subject.getUser().principal() + "_suffix"),
            future
        );
        final ElasticsearchException e = expectThrows(ElasticsearchException.class, future::actionGet);
        assertThat(e.getMessage(), containsString("cannot create new profile for [" + subject.getUser().principal() + "]"));
        assertThat(
            e.getMessage(),
            containsString("suffix setting of domain [" + subject.getRealm().getDomain().name() + "] does not support auto-increment")
        );
    }
    public void testBuildSearchRequest() {
        final String name = randomAlphaOfLengthBetween(0, 8);
        final int size = randomIntBetween(0, Integer.MAX_VALUE);
        final SuggestProfilesRequest.Hint hint = SuggestProfilesRequestTests.randomHint();
        final SuggestProfilesRequest suggestProfilesRequest = new SuggestProfilesRequest(Set.of(), name, size, hint);
        final TaskId parentTaskId = new TaskId(randomAlphaOfLength(20), randomNonNegativeLong());
        final SearchRequest searchRequest = profileService.buildSearchRequestForSuggest(suggestProfilesRequest, parentTaskId);
        assertThat(searchRequest.getParentTask(), is(parentTaskId));
        final SearchSourceBuilder searchSourceBuilder = searchRequest.source();
        assertThat(
            searchSourceBuilder.sorts(),