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
assertThat(responseMap.get("errors"), nullValue());
        @SuppressWarnings("unchecked")
        final List<Map<String, Object>> profiles = (List<Map<String, Object>>) responseMap.get("profiles");
        assertThat(profiles.size(), equalTo(1));
        final Map<String, Object> profileMap = profiles.get(0);
        assertThat(profileMap.get("uid"), equalTo(uid));
        return profileMap;
    }
    private Map<String, Object> doGetProfiles(List<String> uids, @Nullable String dataKey) throws IOException {
        final Request getProfilesRequest = new Request("GET", "_security/profile/" + Strings.collectionToCommaDelimitedString(uids));
        if (dataKey != null) {
            getProfilesRequest.addParameter("data", dataKey);
        }
        final Response getProfilesResponse = adminClient().performRequest(getProfilesRequest);
        assertOK(getProfilesResponse);
        return responseAsMap(getProfilesResponse);
    }
    private void doSetEnabled(String uid, boolean enabled) throws IOException {
        final Request setEnabledRequest = new Request(
            randomFrom("PUT", "POST"),
            "_security/profile/" + uid + "/_" + (enabled ? "enable" : "disable")
        );
        adminClient().performRequest(setEnabledRequest);
    }
    @SuppressWarnings("unchecked")
    private Map<String, Object> castToMap(Object o) {
        return (Map<String, Object>) o;
    }
}