Check if new or legacy export file exist first before downloading

- If a file with the new naming system already exists, then don't do anything. (e.g. `e79ffde3-7fb4-4af3-9ec8-df648b391597@7.1.xml`)
- If a file with the legacy naming system exists, then hardlink it (e.g. hardlink `col11406-1.7.offline.zip` to `e79ffde3-7fb4-4af3-9ec8-df648b391597@7.1.zip`)
- If we can't find any files, then download it from legacy