chore: move the go code into a subfolder

apps/api/internal/notification/channels/channel.go

@@ -0,0 +1,20 @@
+package channels
+
+import "github.com/zitadel/zitadel/internal/eventstore"
+
+type Message interface {
+	GetTriggeringEventType() eventstore.EventType
+	GetContent() (string, error)
+}
+
+type NotificationChannel interface {
+	HandleMessage(message Message) error
+}
+
+var _ NotificationChannel = (HandleMessageFunc)(nil)
+
+type HandleMessageFunc func(message Message) error
+
+func (h HandleMessageFunc) HandleMessage(message Message) error {
+	return h(message)
+}