Add using_license_seat attribute to Users API

doc/api/users.md

@@ -170,7 +170,7 @@ GET /users
 ]
 ```
 
-Users on GitLab [Starter, Bronze, or higher](https://about.gitlab.com/pricing/) also see the `shared_runners_minutes_limit`, and `extra_shared_runners_minutes_limit` parameters.
+Users on GitLab [Starter, Bronze, or higher](https://about.gitlab.com/pricing/) also see the `shared_runners_minutes_limit`, `extra_shared_runners_minutes_limit`, and `using_license_seat` parameters.
 
 ```json
 [
@@ -179,6 +179,7 @@ Users on GitLab [Starter, Bronze, or higher](https://about.gitlab.com/pricing/)
     ...
     "shared_runners_minutes_limit": 133,
     "extra_shared_runners_minutes_limit": 133,
+    "using_license_seat": true
     ...
   }
 ]