Core Schema: Alert Type

[Vidushi-GitHub]

Description

For Chime FRB Notices,
alert_type [initial, update, retraction] isn't sufficient.

Acceptance criteria

How about alert_type as [detection, subsequent, update, retraction]?
Subsequent is same event flaring up again.

[shb46]

Instead of adding an alert_type, they could use the known source name as a "classification" property, define a new property "detection _count" and possibly use the "reference" schema to refer to the first or other previous detections.