Owner doesn't have permissions to load challenge if task is assigned to someone

[maxceem]

Steps to reproduce

1. Create a challenge with any non-admin user, for example, with a Topcoder Manager pshah_manager
2. Call GET endpoint for the created challenge using Postman to make sure that pshah_manager user can see the challenge.
3. Use Postman to PATCH the challenge and assign task member with the next body:

   {
     "task": {
        "isTask": true,
        "memberId": "40035291",
        "isAssigned": true
      }
   }

4. Now call GET endpoint again, the access would be denied:

    {
       "message": "You don't have access to view this challenge"
    }
   

The reason for this issue is this security check https://github.com/topcoder-platform/challenge-api/blob/develop/src/services/ChallengeService.js#L924-L929.
We should additionally allow to get tasks to the copilots.

[rootelement]

Fixed in #287