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/qa/profile/src/javaRestTest/java/org/elasticsearch/xpack/security/profile/ProfileIT.java
Map<String, Object> profileHasPrivilegesResponseMap = responseAsMap(profileHasPrivilegesResponse);
        assertThat(profileHasPrivilegesResponseMap.keySet(), contains("has_privilege_uids", "errors"));
        assertThat(((List<String>) profileHasPrivilegesResponseMap.get("has_privilege_uids")), contains(profileUid));
        assertThat(
            profileHasPrivilegesResponseMap.get("errors"),
            equalTo(
                Map.of(
                    "count",
                    1,
                    "details",
                    Map.of("some_missing_profile", Map.of("type", "resource_not_found_exception", "reason", "profile document not found"))
                )
            )
        );
    }
    public void testGetProfiles() throws IOException {
        final List<String> uids = randomList(1, 3, () -> randomAlphaOfLength(20));
        
        final Map<String, Object> responseMap0 = doGetProfiles(uids, null);
        @SuppressWarnings("unchecked")
        final List<Object> profiles0 = (List<Object>) responseMap0.get("profiles");
        assertThat(profiles0, empty());
        final Map<String, Object> errors0 = castToMap(responseMap0.get("errors"));
        assertThat(errors0.get("count"), equalTo(uids.size()));
        final Map<String, Object> errorDetails0 = castToMap(errors0.get("details"));
        assertThat(errorDetails0.keySet(), equalTo(Set.copyOf(uids)));
        errorDetails0.values().forEach(value -> assertThat(castToMap(value).get("reason"), equalTo("profile index does not exist")));
        
        for (String uid : uids) {
            final String source = SAMPLE_PROFILE_DOCUMENT_TEMPLATE.formatted(uid, uid, Instant.now().toEpochMilli());