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/SecurityInfoTransportActionTests.java
private Settings settings;
    private MockLicenseState licenseState;
    private Realms realms;
    private IPFilter ipFilter;
    private CompositeRolesStore rolesStore;
    private NativeRoleMappingStore roleMappingStore;
    private SecurityUsageServices securityServices;
    @Before
    public void init() throws Exception {
        settings = Settings.builder().put("path.home", createTempDir()).build();
        licenseState = mock(MockLicenseState.class);
        realms = mock(Realms.class);
        ipFilter = mock(IPFilter.class);
        rolesStore = mock(CompositeRolesStore.class);
        roleMappingStore = mock(NativeRoleMappingStore.class);
        securityServices = new SecurityUsageServices(realms, rolesStore, roleMappingStore, ipFilter);
    }
    public void testAvailable() {
        SecurityInfoTransportAction featureSet = new SecurityInfoTransportAction(
            mock(TransportService.class),
            mock(ActionFilters.class),
            settings
        );