text: Title: create user-facing cleanlab.data_valuation module
  Body: Move the following method to the cleanlab.data_valuation module, such that it can be a standalone user-facing method:
  
  [cleanlab.datalab.internal.issue_maanger.data_valuation._knn_shapley_score
  ](https://docs.cleanlab.ai/master/_modules/cleanlab/datalab/internal/issue_manager/data_valuation.html#DataValuationIssueManager.find_issues)
  
  