idhub.entrypoint.sh: add send_mail_admins

warn admin that it should re-enter password to keep the service working

docker/idhub.entrypoint.sh

@@ -27,6 +27,9 @@ deployment_strategy() {
                 echo "INFO: detected EXISTING deployment"
                 ./manage.py makemigrations
                 ./manage.py migrate
+
+                # warn admin that it should re-enter password to keep the service working
+                ./manage.py send_mail_admins
         else
                 # move the migrate thing in docker entrypoint
                 #   inspired by https://medium.com/analytics-vidhya/django-with-docker-and-docker-compose-python-part-2-8415976470cc