Add some ways to work with user_email in remove_project_collaborator() and update_project_collaborator()

When using remove_project_collaborator() or update_project_collaborator() one needs user_id which is not exactly easy to get. It can be extracted from list_project_collaborators() which provides the info, but it is not really handy or intuitive.

Either remove_project_collaborator() and update_project_collaborator() should take also user_email besides user_id to allow editing collaborators for project. Or there could be new Endpoint and client function to get user_id from user_email.

先閱讀 remove_project_collaborator()、update_project_collaborator() 和 list_project_collaborators()，了解它們目前如何處理 user_id。釐清預期結果是在現有函式中支援 email，還是提供一個 user_id 查詢端點，然後定義 API 行為以及證明使用所選方案可以正常更新協作者所需的測試。