feat: add notification events handling and MQTT integration

- Implemented notification event publishing with a new NotificationEventPublisher interface.
- Created a noopNotificationEventPublisher for testing purposes.
- Added functionality to publish notification created events via MQTT.
- Introduced a new stream event publisher for handling job logs and updates.
- Added database migration for popup_ads table.
- Created tests for notification events and popup ads functionality.
- Established MQTT connection and publishing helpers for event messages.

internal/transport/mqtt/constants.go

@@ -0,0 +1,14 @@
+package mqtt
+
+import "time"
+
+const (
+	defaultMQTTBrokerURL = "tcp://broker.mqtt-dashboard.com:1883"
+	defaultMQTTPrefix    = "picpic"
+	defaultPublishWait   = 5 * time.Second
+)
+
+type mqttEvent struct {
+	Type    string `json:"type"`
+	Payload any    `json:"payload"`
+}