Goal: High Quota warnings are implemented as notifications that can be sent via email, Slack webhooks, etc. 

Background: Currently quota warnings only appear in the Quay UI, but most customers rely on asynchronous notifications because they don't check the UI on regular basis. Without an proactive notification via supported channel, the user may only become aware of their quota utilization when its too late (Quota exhausted, pushes denied).

Required deliverables

• Have “High Quota” warnings at user-defined levels (e.g. 75%, 80%, 95% etc) that can trigger notifications via email, Slack webhooks, etc. The send methods should be analogous to the notification methods for
• An organization-wide default notification setting for all repositories (new & existing) should allowed to be set
• Organization-level notification settings should also include all existing notification sources
• the email address used for sending an email-based notification must be separately configurable in line with existing email repository notifications