text: Title: update datalab.get_issues("class_imbalance") to include the label of each example
  Body: This dataframe here should indicate the class label of each example
  
  ![Screen Shot 2023-12-15 at 7 54 12 PM](https://github.com/cleanlab/cleanlab/assets/1390638/23051dd3-83d6-48f0-bcfd-c9da9ad6dd25)
  
  Also `datalab.report()` should be updated so that:
  
  ![Screen Shot 2023-12-15 at 7 55 10 PM](https://github.com/cleanlab/cleanlab/assets/1390638/8e4fc46e-e56b-4e98-a4c5-fbc52dfe5581)
  
  Contains an extra line:
  
  > About this issue:
  >        Examples belonging to the most under-represented class in the dataset (class: <name_of_class>)