Assign update timestamps at database level

[leplatrem]

Follow-up of Graham's comment

[grahamalama]

One issue you might run into with these tests:

https://www.postgresql.org/docs/current/functions-datetime.html#FUNCTIONS-DATETIME-CURRENT

Since these functions return the start time of the current transaction, their values do not change during the transaction. This is considered a feature: the intent is to allow a single transaction to have a consistent notion of the “current” time, so that multiple modifications within the same transaction bear the same time stamp.

Since we use this method to set up database tests, which wraps the entire test in a database transaction that rolls back when the test is complete, the automatic updating via #723 or even the use of NOW() may not behave as expected in tests.