fix: Only trigger email_user_submission_confirmation event once per session

[DafyddLlyr]

What's the problem?

• When an application is submitted to multiple locations, the email_user_submission_confirmation event trigger is called multiple times, resulting in multiple emails being sent to applicants from PlanX.
• This is recreatable locally, and can be observed as a pattern via GovNotify or the Hasura event log - we can see grouped events and emails for the same PlanX session

What's the solution?

• Adds a check within the query, so that the trigger is only called once

[github-actions]

Removed vultr server and associated DNS entries

[DafyddLlyr]

Fix multiple confirmation mails being sent for a single submission

[jessicamcinchak]

Perfect, thank you!