Add unsubscribe from notifications link in emails

[skanderm]

Notification emails about detections should probably have a one-click unsubscribe link in the footer. For Orcasite, we also add a 14 day expiration on the unsubscribe tokens: https://github.com/orcasound/orcasite/blob/main/server/lib/orcasite/notifications/resources/subscription.ex#L79

[vicmartine-git]

Hello, I'd like to work on this issue. Are you accepting contributions? If so, how can I gain access to LiveSRKWNotificationSystem resource group so I can configure my local settings? Thank you.