Add basic metrics to user notifications

Created by: artemruts

Description

This PR adds basic metrics to user notifications, specifically:

• when a user opens a notifications dropdown
• when a user clicks on the notification link

User notifications are loaded, tracking cases:

event name: UserNotificationsLoaded payload: see UserNotificationsOpened, payload variations are the same

User opens notifications dropdown, tracking cases:

1. No notifications, everything is synced and up-to-date

   event name: UserNotificationsOpened payload:

   {
     "status": "success"
   }

   Everything is up-to-date demo

   
   

2. No added code hosts

   event name: UserNotificationsOpened payload:

   {
     "status": "NoCodehosts"
   }

   No code hosts demo

   
   

3. No added repositories

   event name: UserNotificationsOpened payload:

   {
     "status": "NoRepos"
   }

   No repos demo

   
   

4. Multiple in-progress and error notifications

   event name: UserNotificationsOpened payload:

   {
     "status":  ["CloningProgress" | "IndexingProgress" | "ExternalServiceSyncError" | "SyncError" | "IndexingError"] 
   }

   multiple notifications demo

   
   

User clicks a notifications link:

event name: UserNotificationsLinkClicked payload:

{
  "href": string,
  "notificationType":  "not-active" | "progress" | "warning" | "success" | "error"
}

notifications link tracking demo

https://user-images.githubusercontent.com/1319181/135966649-78ccfc6c-b4c9-4d5e-a0a0-2e0b53485111.mov

Tests

Tested locally and on .com