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
},
            "application_data": {
              "app1": { "name": "app1" },
              "app2": { "name": "app2" }
            }
          }
        }
        """;
    private ThreadPool threadPool;
    private Client client;
    private SecurityIndexManager profileIndex;
    private ProfileService profileService;
    private Version minNodeVersion;
    @Before
    public void prepare() {
        threadPool = spy(
            new TestThreadPool(
                "api key service tests",
                new FixedExecutorBuilder(
                    Settings.EMPTY,
                    SECURITY_CRYPTO_THREAD_POOL_NAME,
                    1,
                    1000,
                    "xpack.security.crypto.thread_pool",
                    false
                )
            )
        );
        this.client = mock(Client.class);
        when(client.threadPool()).thenReturn(threadPool);