Add support for data deletion of existing deleted users

Log in as Admin. Go to Site administration > Users > Accounts > Add a new user. Add several users. Go to Site administration > Users > Accounts > Bulk user actions. Bulk delete previously created users. Run the scheduled task to create delete data requests for pre-existing deleted users ('php admin/tool/task/cli/schedule_task.php --execute='tool_dataprivacy\task\delete_existing_deleted_users''). Go to Site administration > Users > Privacy and policies > Data requests. Make sure data delete data requests have been created for the deleted users. Additionally make sure that further actions such as viewing, approving and denying these particular requests works as expected.