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
RestController restController,
        ClusterSettings clusterSettings,
        IndexScopedSettings indexScopedSettings,
        SettingsFilter settingsFilter,
        IndexNameExpressionResolver indexNameExpressionResolver,
        Supplier<DiscoveryNodes> nodesInCluster
    ) {
        if (enabled == false) {
            return emptyList();
        }
        return Arrays.asList(
            new RestAuthenticateAction(settings, securityContext.get(), getLicenseState()),
            new RestClearRealmCacheAction(settings, getLicenseState()),
            new RestClearRolesCacheAction(settings, getLicenseState()),
            new RestClearPrivilegesCacheAction(settings, getLicenseState()),
            new RestClearApiKeyCacheAction(settings, getLicenseState()),
            new RestClearServiceAccountTokenStoreCacheAction(settings, getLicenseState()),
            new RestGetUsersAction(settings, getLicenseState()),
            new RestPutUserAction(settings, getLicenseState()),
            new RestDeleteUserAction(settings, getLicenseState()),
            new RestGetRolesAction(settings, getLicenseState()),
            new RestPutRoleAction(settings, getLicenseState()),
            new RestDeleteRoleAction(settings, getLicenseState()),
            new RestChangePasswordAction(settings, securityContext.get(), getLicenseState()),
            new RestSetEnabledAction(settings, getLicenseState()),
            new RestHasPrivilegesAction(settings, securityContext.get(), getLicenseState()),
            new RestGetUserPrivilegesAction(settings, securityContext.get(), getLicenseState()),
            new RestGetRoleMappingsAction(settings, getLicenseState()),
            new RestPutRoleMappingAction(settings, getLicenseState()),
            new RestDeleteRoleMappingAction(settings, getLicenseState()),