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
equalTo(List.of(new ScoreSortBuilder(), new FieldSortBuilder("user_profile.last_synchronized").order(SortOrder.DESC)))
        );
        assertThat(searchSourceBuilder.size(), equalTo(size));
        assertThat(searchSourceBuilder.query(), instanceOf(BoolQueryBuilder.class));
        final BoolQueryBuilder query = (BoolQueryBuilder) searchSourceBuilder.query();
        if (Strings.hasText(name)) {
            assertThat(
                query.must(),
                equalTo(
                    List.of(
                        QueryBuilders.multiMatchQuery(
                            name,
                            "user_profile.user.username",
                            "user_profile.user.username._2gram",
                            "user_profile.user.username._3gram",
                            "user_profile.user.full_name",
                            "user_profile.user.full_name._2gram",
                            "user_profile.user.full_name._3gram",
                            "user_profile.user.email"
                        ).type(MultiMatchQueryBuilder.Type.BOOL_PREFIX).fuzziness(Fuzziness.AUTO)
                    )
                )
            );
        } else {
            assertThat(query.must(), empty());
        }
        if (hint != null) {
            final List<QueryBuilder> shouldQueries = new ArrayList<>(query.should());
            if (hint.getUids() != null) {
                assertThat(shouldQueries.remove(0), equalTo(QueryBuilders.termsQuery("user_profile.uid", hint.getUids())));