The Sia gateway had a bug with uploading that prevented the user's uploads
from reaching the Sia backend. The PutObject function called fsRemoveFile at
the end of the function, which didn't give the Sia backend enough time to
upload the file to the Sia network.
This adds a goroutine that watches the file upload progress and doesn't delete
the file until the upload reaches 100% complete.
Note that this solution has the limitation where if the minio process dies in
the middle of upload, it will leave orphaned files in the SIA_TEMP directory
that the user will need to remove manually.