In the "main-app" module, the `HelloInterface` service instance, `HelloModules`, was just being treated like an ordinary class that was exported from the "hello.modules" module. The code was not treating the class as a service class. This is not a good example of how services are used.
This commit makes use of the `ServiceLoader` class, which provides access to the `HelloInterface` instance as defined in the "hello.modules" module. This serves as a better example for how services are used.
