This commit improves the check that a user has set a welcome email campaign (a task in product discovery task list)
by checking also for automation flows that are triggered by new subscriber or user and contain
send email action.
[MAILPOET-4827]
We should listen to mailpoet_segment_subscribed to start the trigger.
This means the subscriber is confirmed. And it removes the fatal error
which was produced by not finding the $segment during signup.
[MAILPOET-4772]
[MAILPOET-4773]
