Add crud endpoints for notifications (#801)

Co-authored-by: kolaente <k@knt.li>
Reviewed-on: https://kolaente.dev/vikunja/api/pulls/801
Co-authored-by: konrad <konrad@kola-entertainments.de>
Co-committed-by: konrad <konrad@kola-entertainments.de>

pkg/notifications/notification_test.go

@@ -44,6 +44,11 @@ func (n *testNotification) ToDB() interface{} {
 	return data
 }
 
+// Name returns the name of the notification
+func (n *testNotification) Name() string {
+	return "test.notification"
+}
+
 type testNotifiable struct {
 }