InMemoryTestContainer does not call "onStartup" and "onShutdown"

In the "start" and "stop" methods of the TestContainer, the internal ApplicationHandler's "onStartup" and onShutdown" methods need to be called to make sure that registered ContainerLifecycleListeners are executed.

```
@Override
public void start() {
if (started.compareAndSet(false, true)) {
LOGGER.log(Level.FINE, "Starting InMemoryContainer...");
// this line needs to be added:
appHandler.onStartup(null);
} else {
LOGGER.log(Level.WARNING, "Ignoring start request - InMemoryTestContainer is already started.");
}
}

@Override
public void stop() {
if (started.compareAndSet(true, false)) {
LOGGER.log(Level.FINE, "Stopping InMemoryContainer...");
// this line needs to be added:
appHandler.onShutdown(null);
} else {
LOGGER.log(Level.WARNING, "Ignoring stop request - InMemoryTestContainer is already stopped.");
}
}
```