Manager: set default MQTT topic prefix to 'flamenco'

Set the default MQTT topic prefix to 'flamenco'. It can still be overridden
by the config in the YAML file, but it's nice to have a sensible default
when people don't configure this.

internal/manager/config/defaults.go

@@ -4,6 +4,7 @@ import (
 	"runtime"
 	"time"
 
+	"projects.blender.org/studio/flamenco/internal/manager/eventbus"
 	shaman_config "projects.blender.org/studio/flamenco/pkg/shaman/config"
 )
 
@@ -39,6 +40,13 @@ var defaultConfig = Conf{
 
 		BlocklistThreshold:         3,
 		TaskFailAfterSoftFailCount: 3,
+
+		MQTT: MQTTConfig{
+			Client: eventbus.MQTTClientConfig{
+				ClientID:    eventbus.MQTTDefaultClientID,
+				TopicPrefix: eventbus.MQTTDefaultTopicPrefix,
+			},
+		},
 	},
 
 	Variables: map[string]Variable{

internal/manager/eventbus/mqtt_client.go

@@ -18,7 +18,9 @@ import (
 )
 
 const (
-	defaultClientID   = "flamenco"
+	MQTTDefaultTopicPrefix = "flamenco"
+	MQTTDefaultClientID    = "flamenco"
+
 	keepAlive         = 30 // seconds
 	connectRetryDelay = 10 * time.Second
 
@@ -63,7 +65,7 @@ func NewMQTTForwarder(config MQTTClientConfig) *MQTTForwarder {
 		return nil
 	}
 	if config.ClientID == "" {
-		config.ClientID = defaultClientID
+		config.ClientID = MQTTDefaultClientID
 	}
 
 	brokerURL, err := url.Parse(config.BrokerURL)