Don't send news when they're overdue

Motivation

Currently, the push notification sending management command sends all push notifications that are scheduled for any point in time in the past, but did not yet get sent:

integreat-cms/integreat_cms/core/management/commands/send_push_notifications.py

Line 57 in 46bfc49

scheduled_send_date__lte=timezone.now(),

This means, that even if the command fails for a longer period of time, as soon as it's starting to work again, very old messages might be sent, which could lead to confusion.

Proposed Solution

Add a new setting for the maximum overdue time (e.g. 1 or 2 days)
Only send news which are scheduled for a date in this time frame

Optionally: Indicate in the CMS that a scheduled message is overdue and won't get sent anymore, even if the command would start working again.

User Story

As an end user, I don't want to receive old news