cubicweb #2119248 Notification are sent too early [validation pending]

At the moment notification are sent a pre-commit time. This may result in notification sent for change rollbacked by later operation.

I consider sending notification for stuff which did not actually happend as a bug.

prioritynormal
typebug
done in3.14.4
load0.200
load left0.000
closed by#884405bf3621 [email notifications] send notification at post-commit time (closes #2119248)