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/main/java/org/elasticsearch/xpack/security/profile/ProfileService.java
builder.startObject();
                {
                    if (false == request.getLabels().isEmpty()) {
                        builder.field("labels", request.getLabels());
                    }
                    if (false == request.getData().isEmpty()) {
                        builder.field("application_data", request.getData());
                    }
                }
                builder.endObject();
            }
            builder.endObject();
        } catch (IOException e) {
            listener.onFailure(e);
            return;
        }
        doUpdate(
            buildUpdateRequest(request.getUid(), builder, request.getRefreshPolicy(), request.getIfPrimaryTerm(), request.getIfSeqNo()),
            listener.map(updateResponse -> AcknowledgedResponse.TRUE)
        );
    }
    public void suggestProfile(SuggestProfilesRequest request, TaskId parentTaskId, ActionListener<SuggestProfilesResponse> listener) {
        tryFreezeAndCheckIndex(listener.map(response -> {
            assert response == null : "only null response can reach here";
            return new SuggestProfilesResponse(
                new SuggestProfilesResponse.ProfileHit[] {},
                0,
                new TotalHits(0, TotalHits.Relation.EQUAL_TO)
            );
        })).ifPresent(frozenProfileIndex -> {