feat(alerting): support for attached graphs in alert notifications

closes #6183

pkg/models/notifications.go

@@ -5,11 +5,12 @@ import "errors"
 var ErrInvalidEmailCode = errors.New("Invalid or expired email code")
 
 type SendEmailCommand struct {
-	To       []string
-	Template string
-	Data     map[string]interface{}
-	Massive  bool
-	Info     string
+	To           []string
+	Template     string
+	Data         map[string]interface{}
+	Massive      bool
+	Info         string
+	EmbededFiles []string
 }
 
 type SendEmailCommandSync struct {