Add a error log for alert tasks.

Many of the team members do not look at emails from zendesk, adding a current_app.logger.error message for things we care about to give developers a better chance of seeing them.
I have purposely not added an erro log for `check_for_services_with_high_failure_rates_or_sending_to_tv_numbers` because it's not something we need to look at immediately.

app/celery/broadcast_message_tasks.py

@@ -150,6 +150,7 @@ def send_broadcast_event(broadcast_event_id):
             ticket_type=zendesk_client.TYPE_INCIDENT,
             p1=True,
         )
+        current_app.logger.error(message)
 
     for provider in broadcast_event.service.get_available_broadcast_providers():
         send_broadcast_provider_message.apply_async(