EE: Refactor Project#create_or_update_import_data

What does this MR do?

This was originally added in CE MR https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/23701. Despite being merged into EE (26378511), somehow the changes themselves got lost. I'm starting to suspect our merging code is to blame after all, so I have disabled that in the mean time. This MR simply re-adds the changes.

Does this MR meet the acceptance criteria?

• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.
• EE specific content should be in the top level /ee folder
• Security reports checked/validated by reviewer