feat: add stdout and filesystem notification channels (#2925)

* feat: add filesystem and stdout notification channels

* configure through env vars

* compile

* feat: add compact option for debug notification channels

* fix channel mock generation

* avoid sensitive information in error message

Co-authored-by: Livio Amstutz <livio.a@gmail.com>

* add review improvements

Co-authored-by: Livio Amstutz <livio.a@gmail.com>

internal/notification/channels/channel.go

@@ -0,0 +1,17 @@
+package channels
+
+type Message interface {
+	GetContent() string
+}
+
+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)
+}