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
private final SetOnce<IPFilter> ipFilter = new SetOnce<>();
    private final SetOnce<AuthenticationService> authcService = new SetOnce<>();
    private final SetOnce<SecondaryAuthenticator> secondayAuthc = new SetOnce<>();
    private final SetOnce<AuditTrailService> auditTrailService = new SetOnce<>();
    private final SetOnce<SecurityContext> securityContext = new SetOnce<>();
    private final SetOnce<ThreadContext> threadContext = new SetOnce<>();
    private final SetOnce<TokenService> tokenService = new SetOnce<>();
    private final SetOnce<SecurityActionFilter> securityActionFilter = new SetOnce<>();
    private final SetOnce<SharedGroupFactory> sharedGroupFactory = new SetOnce<>();
    private final SetOnce<DocumentSubsetBitsetCache> dlsBitsetCache = new SetOnce<>();
    private final SetOnce<List<BootstrapCheck>> bootstrapChecks = new SetOnce<>();
    private final List<SecurityExtension> securityExtensions = new ArrayList<>();
    private final SetOnce<Transport> transportReference = new SetOnce<>();
    private final SetOnce<ScriptService> scriptServiceReference = new SetOnce<>();
    public Security(Settings settings) {
        this(settings, Collections.emptyList());
    }
    Security(Settings settings, List<SecurityExtension> extensions) {
        
        this.settings = settings;
        
        this.enabled = XPackSettings.SECURITY_ENABLED.get(settings);
        this.systemIndices = new SecuritySystemIndices();
        this.nodeStartedListenable = new ListenableFuture<>();
        if (enabled) {
            runStartupChecks(settings);
            Automatons.updateConfiguration(settings);
        } else {
            this.bootstrapChecks.set(Collections.emptyList());
        }