Remove temp file when file is successfully uploaded

[aaronofinn]

When uploading a file for a task that already has a file, it moves the old file to a temp directory. But on a successful upload, the temporary file still stays there so this is just a small fix to remove that temp file when the operation is successful.

How to reproduce (before this fix)

curl -c /tmp/c.txt -X POST http://localhost:3000/api/auth/login \
  -H "Content-Type: application/json" \
  -d '{"email":"basic@example.com","password":"Password123$"}'

# upload once
curl -b /tmp/c.txt -X POST http://localhost:3000/api/tasks/1/upload -F "file=@/path/to/image.png"
# upload again onto the same task
curl -b /tmp/c.txt -X POST http://localhost:3000/api/tasks/1/upload -F "file=@/path/to/image.png"

ls uploads/tasks/temp/
# a leftover temp-<random>-1_image.png sits here after the second upload succeeded

Checklist

• run npm run test && npm run benchmark --if-present
• tests and/or benchmarks are included
• documentation is changed or added
• commit message and code follows the Developer's Certification of Origin
  and the Code of conduct

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[jean-michelet]

I think we should remove this feature of file upload, I tried to do this to illustrate the use of the multipart plugin and streams usage, but there are several system design flaws that fixing theme would make to much noise for a basic demo.