To avoid ever using the axe again as in T110438: Evaluate lists with large moderation queues, I suggest that we change the default for max_days_to_hold from 0 (unlimited) to 365 days or a similarly huge number.

There is little point in approving or even recovering a message hold for moderation, many months after it is sent: a message with a date of many months earlier will behave badly in most clients and look suspicious to spam filters as well.

Setting a non-zero limit prevent the moderation queues from being *infinite*.