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/Security.java
throw new IllegalArgumentException(sb.toString());
        }
    }
    @Override
    public List<TransportInterceptor> getTransportInterceptors(NamedWriteableRegistry namedWriteableRegistry, ThreadContext threadContext) {
        if (enabled == false) { 
            return Collections.emptyList();
        }
        return Collections.singletonList(new TransportInterceptor() {
            @Override
            public <T extends TransportRequest> TransportRequestHandler<T> interceptHandler(
                String action,
                String executor,
                boolean forceExecution,
                TransportRequestHandler<T> actualHandler
            ) {
                assert securityInterceptor.get() != null;
                return securityInterceptor.get().interceptHandler(action, executor, forceExecution, actualHandler);
            }
            @Override
            public AsyncSender interceptSender(AsyncSender sender) {
                assert securityInterceptor.get() != null;
                return securityInterceptor.get().interceptSender(sender);
            }
        });
    }
    @Override
    public Map<String, Supplier<Transport>> getTransports(
        Settings settings,
        ThreadPool threadPool,