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/smtp/config.go

@@ -0,0 +1,18 @@
+package smtp
+
+type EmailConfig struct {
+	SMTP     SMTP
+	Tls      bool
+	From     string
+	FromName string
+}
+
+type SMTP struct {
+	Host     string
+	User     string
+	Password string
+}
+
+func (smtp *SMTP) HasAuth() bool {
+	return smtp.User != "" && smtp.Password != ""
+}