Error disclosure on Project Import

From #54857 (closed). When an error is encountered importing a project, the error message displayed gives file directory structure information.

Through the API:

Find the real path of link.gitignore

Luckily, Gitlab stores import errors in database and provides another API with the error messages where we can find the real path of link.gitignore

$ curl -H "Private-Token: $(cat tkn.nya)" http://10.26.0.3/api/v4/projects/27/import
{
  "id": 27,
  "description": null,
  "name": "interesting-36f24022b707434f2f060c4a3559216f",
  "name_with_namespace": "Administrator / interesting-36f24022b707434f2f060c4a3559216f",
  "path": "interesting-36f24022b707434f2f060c4a3559216f",
  "path_with_namespace": "root/interesting-36f24022b707434f2f060c4a3559216f",
  "created_at": "2018-12-04T11:10:59.269Z",
  "import_status": "failed",
  "import_error": "Error importing repository  into root/interesting-36f24022b707434f2f060c4a3559216f - Permission denied @ unlink_internal - /var/opt/gitlab/gitlab-rails/shared/tmp/project_exports/root/interesting-36f24022b707434f2f060c4a3559216f/8cef47205d875e9e9528a844ce20e092/uploads/link.gitignore"
}

Through the UI: One other note, we present the full path to the file in the UI. Technically, the api call in File the Real Path is not needed.