Add message retention parameter

[vicmarbev]

🎩 What?

Set a default value for subscriptions message retention by default to 24 hours. You can set a custom value by specifying the parameter MESSAGE_RETENTION_DURATION in your Django project.

🤔 Why?

In Google Pub/Sub pricing page, they state that:

Note: Starting from June 30, 2024, you are going to incur charges for retaining unacknowledged messages with subscriptions for more than 24 hours. If you are able to process the messages within 24 hours, the additional charges are not calculated. To know more, see message retention duration.

🔗 Related issue

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