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 RestProfileHasPrivilegesAction(settings, securityContext.get(), getLicenseState()),
            new RestGetProfilesAction(settings, getLicenseState()),
            new RestActivateProfileAction(settings, getLicenseState()),
            new RestUpdateProfileDataAction(settings, getLicenseState()),
            new RestSuggestProfilesAction(settings, getLicenseState()),
            new RestEnableProfileAction(settings, getLicenseState()),
            new RestDisableProfileAction(settings, getLicenseState())
        );
    }
    @Override
    public Map<String, Processor.Factory> getProcessors(Processor.Parameters parameters) {
        return Collections.singletonMap(
            SetSecurityUserProcessor.TYPE,
            new SetSecurityUserProcessor.Factory(securityContext::get, settings)
        );
    }
    @Override
    public void onNodeStarted() {
        this.nodeStartedListenable.onResponse(null);
    }
    /**
     * Realm settings were changed in 7.0. This method validates that the settings in use on this node match the new style of setting.
     * In 6.x a realm config would be
     * <pre>
     *   xpack.security.authc.realms.file1.type: file
     *   xpack.security.authc.realms.file1.order: 0
     * </pre>
     * In 7.x this realm should be
     * <pre>
     *   xpack.security.authc.realms.file.file1.order: 0