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/publish_helpers.go

@@ -0,0 +1,64 @@
+package mqtt
+
+import (
+	"encoding/json"
+	"fmt"
+	"time"
+
+	pahomqtt "github.com/eclipse/paho.mqtt.golang"
+	"stream.api/pkg/logger"
+)
+
+func connectPahoClient(broker, clientID string) (pahomqtt.Client, error) {
+	opts := pahomqtt.NewClientOptions().
+		AddBroker(broker).
+		SetClientID(clientID).
+		SetAutoReconnect(true).
+		SetConnectRetry(true).
+		SetKeepAlive(60 * time.Second).
+		SetPingTimeout(10 * time.Second).
+		SetConnectRetryInterval(3 * time.Second)
+
+	client := pahomqtt.NewClient(opts)
+	token := client.Connect()
+	if ok := token.WaitTimeout(defaultPublishWait); !ok {
+		return nil, fmt.Errorf("mqtt connect timeout")
+	}
+	if err := token.Error(); err != nil {
+		return nil, err
+	}
+
+	return client, nil
+}
+
+func publishMQTTEvent(client pahomqtt.Client, appLogger logger.Logger, prefix string, event mqttEvent) {
+	if client == nil {
+		return
+	}
+
+	if err := publishMQTTJSON(client, fmt.Sprintf("%s/events", prefix), event); err != nil {
+		appLogger.Error("Failed to publish MQTT event", "error", err, "type", event.Type)
+	}
+}
+
+func publishMQTTJSON(client pahomqtt.Client, topic string, payload any) error {
+	if client == nil {
+		return nil
+	}
+	encoded, err := json.Marshal(payload)
+	if err != nil {
+		return err
+	}
+	return publishPahoMessage(client, topic, encoded)
+}
+
+func publishPahoMessage(client pahomqtt.Client, topic string, payload []byte) error {
+	if client == nil {
+		return nil
+	}
+	token := client.Publish(topic, 0, false, payload)
+	if ok := token.WaitTimeout(defaultPublishWait); !ok {
+		return fmt.Errorf("mqtt publish timeout")
+	}
+	return token.Error()
+}