Add webhook v3 types

[icholy]

I originally had this function too, but I didn't find it very useful.

// ParseEventData parses the event data into the correct type.
func ParseEventData(e Event) (any, error) {
	var data any
	switch e.EventType {
	case "incident.acknowledged", "incident.annotated", "incident.delegated",
		"incident.escalated", "incident.priority_updated", "incident.reassigned",
		"incident.reopened", "incident.triggered", "incident.unacknowledged":
		data = &IncidentData{}
	case "incident.conference_bridge.updated":
		data = &IncidentConferenceBridgeData{}
	case "incident.custom_field_values.updated":
		data = &IncidentFieldValuesData{}
	case "incident.responder.added", "incident.responder.replied":
		data = &IncidentResponderData{}
	case "incident.status_update_published":
		data = &IncidentStatusUpdateData{}
	case "incident.workflow.started", "incident.workflow.completed":
		data = &IncidentWorkflowInstanceData{}
	case "pagey.ping":
		data = &PageyData{}
	default:
		return nil, fmt.Errorf("unrecognized event type: %q", e.EventType)
	}
	if err := json.Unmarshal(e.Data, data); err != nil {
		return nil, err
	}
	return data, nil
}