Recreate backup transfer device message for a week after backup transfer ends

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On backup transfer, config option should be written with a timestamp of the last backup transfer. For a week after backup transfer, the message created in #4301 should be recreated to prevent its deletion.

This does not protect against direct database modification, but if attacker can modify the database, they can as well copy the database with their own tools that bypass any protections.

To protect against rewinding time back before doing backup transfer, timestamp should be checked not to be in the past compared to the previous backup, the last received message and other similar timestamps.