Cloud synchronization

While nRF Cloud is connected, main keeps a periodic timer on a dedicated workqueue (CONFIG_APP_MAIN_SYNC_INTERVAL_SECONDS, default 600 seconds). Each synchronization runs through a sequence of substates, waiting for the current step to finish before starting the next:

1. Sends a demo JSON device message on cloud_chan (payload: {"appId":"SMHA","messageType":"DATA","data":"hello"}), then waits for CLOUD_MESSAGE_SENT.
2. Publishes LOCATION_SEARCH_TRIGGER on location_chan when the application is built with the location overlay (CONFIG_APP_LOCATION), then waits for LOCATION_SEARCH_DONE.
3. Publishes CLOUD_SHADOW_POLL_REQUEST on cloud_chan to pick up any desired configuration from the device shadow, then waits for CLOUD_SHADOW_POLLED.
4. Publishes FOTA_POLL_REQUEST on fota_chan to check for firmware updates, then waits for FOTA_ABORTED or enters the FOTA download state on FOTA_STARTING.
5. Publishes CLOUD_MEMFAULT_POST_REQUEST on cloud_chan to post any pending Memfault data, then waits for CLOUD_MEMFAULT_POSTED.

An initial synchronization runs immediately on cloud connect. The timer is cancelled when the cloud disconnects. A new periodic trigger is only acted on while main is idle between synchronizations.

During the location step, the location module scans for Wi-Fi access points and publishes the result as LOCATION_CLOUD_REQUEST, which main forwards to the cloud module. The cloud module resolves it into a position with an nRF Cloud CoAP ground-fix request and logs the position together with a Google Maps URL. Main does not advance past the location step until LOCATION_SEARCH_DONE is published.