With the new unique parameter added in the action scheduler 3.5.0 the
as_schedule_single_action that schedules an immediate action
seems to be more convenient for the action scheduler.
We get better control over the scheduling of subsequent runs.
Note: We don't want to use the async action that is also executed immediately,
but it has the highest priority and we don't want to block actions scheduled by other plugins.
[MAILPOET-4684]
