Series Request Email Notification

User Story
As a physician or emergency department leader, I only want to receive a single notification email for a new series request, instead of repeated emails for each sub-request—particularly when new instances connect and existing requests get polled.

Short Description

- Currently, an email is sent for every unanswered series sub-request.
- Additionally, when a new instance is connected and existing requests are polled, it triggers emails for each outstanding sub-request.
- This results in unnecessary multiple notifications, leading to spam and reduced efficiency.
- The goal is to send just one initial notification email per series request.

Acceptance Criteria
- Only one notification email is generated when a new series request is polled by the AKTIN DWH.
- No additional emails are sent for individual sub-requests within the series.
- Connecting a new instance or polling existing requests does not generate repeated notification emails.

Additional Notes
- Future improvements could include configurable notification settings, allowing users to opt in or out of sub-request notifications.
- For the initial implementation, the focus is on preventing multiple emails caused by each sub-request within a series.