fix: Handle unique file list correctly

[DafyddLlyr]

What's the problem?

• When constructing a FileList for display to the user, we want this to only contain unique files (by name)
• We're experiencing a bug where a file is missing from the FileList
  • There are two FileTypes with the same name
  • Only one of their conditions is met
  • Neither appear in the final list ❌
• Described in detail with example flow here on OSL Slack

What's the cause?

• The unique list of file names we maintain does not check if the file has been added or not to the FileList

What's the solution?

• Check if a file is added by the populateFileList() function
• Only count it as a unique file if added to our FileList

Demo

Broken flow on prod - https://editor.planx.uk/testing/upload-and-label-recommended-test ❌
Fixed flow on pizza - https://2328.planx.pizza/testing/upload-and-label-recommended-test ✅

[github-actions]

Removed vultr server and associated DNS entries

[DafyddLlyr]

August has given this the green light 🟢