Show queue limit error message

[moujar]

Creating a new queue after reaching the limit of 5 queues only displays a generic error message:

"An error occurred!"

This message does not explain the actual reason for the failure, even though the backend returns a clear error.

Current behavior

• The user submits the Create Queue form.

• A generic error message:

  "An error occurred!"

• The browser's Network tab shows the actual API response:

HTTP 403
{
  "detail": "User has reached queue limit!"
}

[Didayolo]

@ihsaan-ullah @moujar Also, when at the limit (5 queues) we can't add new collaborators

And we should increase this limit because it's resource free (#2491)

[ihsaan-ullah]

@Didayolo fixed the collaborators issue and user search issue in latest commit.