Don't immediately remove notifications from notification trays (#4773)

Let the notifications go into browser/OS notification trays so users can click on them from there if they miss the initial notification. Modern browsers generally use OS notifications so the user is in control of the notification at the OS level.

client/app/services/notifications.js

@@ -33,9 +33,6 @@ function showNotification(title, content) {
     body: content,
     icon: redashIconUrl,
   });
-  setTimeout(() => {
-    notification.close();
-  }, 3000);
   notification.onclick = function onClick() {
     window.focus();
     this.close();