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
new RestGetTokenAction(settings, getLicenseState()),
            new RestInvalidateTokenAction(settings, getLicenseState()),
            new RestGetCertificateInfoAction(),
            new RestSamlPrepareAuthenticationAction(settings, getLicenseState()),
            new RestSamlAuthenticateAction(settings, getLicenseState()),
            new RestSamlLogoutAction(settings, getLicenseState()),
            new RestSamlInvalidateSessionAction(settings, getLicenseState()),
            new RestSamlCompleteLogoutAction(settings, getLicenseState()),
            new RestSamlSpMetadataAction(settings, getLicenseState()),
            new RestOpenIdConnectPrepareAuthenticationAction(settings, getLicenseState()),
            new RestOpenIdConnectAuthenticateAction(settings, getLicenseState()),
            new RestOpenIdConnectLogoutAction(settings, getLicenseState()),
            new RestGetBuiltinPrivilegesAction(settings, getLicenseState()),
            new RestGetPrivilegesAction(settings, getLicenseState()),
            new RestPutPrivilegesAction(settings, getLicenseState()),
            new RestDeletePrivilegesAction(settings, getLicenseState()),
            new RestCreateApiKeyAction(settings, getLicenseState()),
            new RestUpdateApiKeyAction(settings, getLicenseState()),
            new RestBulkUpdateApiKeyAction(settings, getLicenseState()),
            new RestGrantApiKeyAction(settings, getLicenseState()),
            new RestInvalidateApiKeyAction(settings, getLicenseState()),
            new RestGetApiKeyAction(settings, getLicenseState()),
            new RestQueryApiKeyAction(settings, getLicenseState()),
            new RestDelegatePkiAuthenticationAction(settings, getLicenseState()),
            new RestCreateServiceAccountTokenAction(settings, getLicenseState()),
            new RestDeleteServiceAccountTokenAction(settings, getLicenseState()),
            new RestGetServiceAccountCredentialsAction(settings, getLicenseState()),
            new RestGetServiceAccountAction(settings, getLicenseState()),
            new RestKibanaEnrollAction(settings, getLicenseState()),
            new RestNodeEnrollmentAction(settings, getLicenseState()),