Implement the log delivery target (closes #70)

internal/delivery/engine.go

@@ -1006,8 +1006,11 @@ func (e *Engine) deliverLog(
 		"webhook event delivered to log target",
 		"delivery_id", d.ID,
 		"event_id", d.EventID,
+		"webhook_id", d.Event.WebhookID,
+		"entrypoint_id", d.Event.EntrypointID,
 		"target_id", d.TargetID,
 		"target_name", d.Target.Name,
+		"outcome", database.DeliveryStatusDelivered,
 		"method", d.Event.Method,
 		"content_type", d.Event.ContentType,
 		"body_length", len(d.Event.Body),