[Bug] Support overriding defaultTitle for Notifications send via Alerting

[AWSHurneyt]

Is your feature request related to a problem?
When the migration of destinations to the Notifications plugin that happened in OS 2.0, the subject line of migrated Alerting trigger action messages have been replaced with the defaultTitle "Alerting-Notification Action" when using SNS to send the emails. The old subject line then appears in the message body.

What solution would you like?
Ideally, if a subject line is populated, Notifications should use that for the email subject instead of the defaultTitle.

Workarounds

1. Users can setup an SES Notification Channel which takes in the title as the subject.

[adamdepollo]

Commenting because this is an urgent fix for my team. We have near 100 alerts that have been impacted by this and switching everything over to SES in the interim will be a big lift.

[uroskarama]

@praveensameneni @adamdepollo this change on alerting plugin should produce the desired behavior

[praveensameneni]

We have a code fix in the works that will be merged today

[qreshi]

Transferred this issue to the Alerting plugin repo as that's where the defaultTitle override needed to occur.

[qreshi]

Closing issue as the change has been merged in.