Send Owner email max once per day

What does this MR do and why?

Relates to https://gitlab.com/gitlab-org/gitlab/-/issues/441796. In this MR, we want to make sure that the all seats used email is only sent max once per day. To achieve it, we're adding a new column last_seat_all_used_seats_notification_at to the namespace_limits. When the relevant events occur, we'll only send the mail if 1) last_seat_all_used_seats_notification_at is nil or 2) if we didn't send one already in the 1 day time frame.

The following is produced from running the specs:

UPDATE "namespace_limits" SET "last_seat_all_used_seats_notification_at" = '2024-05-08 08:40:29.076117' WHERE "namespace_limits"."namespace_id" = 948

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