Add new task to alert about created email / sms

This will log an error when email or SMS notifications have been
stuck in 'created' for too long - normally they should be 'sending'
in seconds, noting that we have a goal of < 10s wait time for most
notifications being processed our platform.

In the next commits we'll decouple similar functionality from the
existing 'timeout-sending-notifications' task.

app/celery/scheduled_tasks.py

@@ -30,6 +30,7 @@ from app.dao.jobs_dao import (
     find_missing_row_for_job,
 )
 from app.dao.notifications_dao import (
+    dao_check_notifications_still_in_created,
     dao_old_letters_with_created_status,
     dao_precompiled_letters_still_pending_virus_check,
     is_delivery_slow_for_providers,
@@ -118,6 +119,19 @@ def switch_current_sms_provider_on_slow_delivery():
                 dao_reduce_sms_provider_priority(provider_name, time_threshold=timedelta(minutes=10))
 
 
+@notify_celery.task(name='raise-alert-if-email-sms-still-in-created')
+def raise_alert_if_email_sms_still_in_created():
+    alert_above_age = current_app.config.get('CREATED_NOTIFICATIONS_ALERT_AGE')
+    still_in_created = dao_check_notifications_still_in_created(alert_above_age)
+    message = f"{still_in_created} notifications are still in 'created'."
+
+    if still_in_created == 0:
+        current_app.logger.info(message)
+        return
+
+    current_app.logger.error(message)
+
+
 @notify_celery.task(name='tend-providers-back-to-middle')
 def tend_providers_back_to_middle():
     dao_adjust_provider_priority_back_to_resting_points()