[nrfconnect] new: sleepy behaviour for lighting app (#23935)

* new: sleepy behaviour for lighting app

* chg: restyle

* chg: removed prj_sleepy.conf. Left changes to AppTask.cpp to allow building sample using CSL

* fix: should keep the router thread device on the basic use case for lighting

examples/lighting-app/nrfconnect/main/AppTask.cpp

@@ -156,7 +156,13 @@ CHIP_ERROR AppTask::Init()
  return err;
  }
 
+#if CONFIG_CHIP_THREAD_SSED
+ err = ConnectivityMgr().SetThreadDeviceType(ConnectivityManager::kThreadDeviceType_SynchronizedSleepyEndDevice);
+#elif CONFIG_OPENTHREAD_MTD_SED
+ err = ConnectivityMgr().SetThreadDeviceType(ConnectivityManager::kThreadDeviceType_SleepyEndDevice);
+#else
  err = ConnectivityMgr().SetThreadDeviceType(ConnectivityManager::kThreadDeviceType_Router);
+#endif
 
  if (err != CHIP_NO_ERROR)
  {