drime: fix uploads of 100..200M files

At some point Drime recommended 200M for the upload cutoff for
switching to multipart upload. However uploads have stopped working
using single part upload for 100..200Mish files.

Their docs now recommend 5M as the cutoff for multipart upload so this
changes the default.

backend/drime/drime.go

@@ -55,7 +55,7 @@ const (
 	rootURL             = baseURL + "api/v1"
 	maxUploadParts      = 10000 // maximum allowed number of parts in a multi-part upload
 	minChunkSize        = fs.SizeSuffix(1024 * 1024 * 5)
-	defaultUploadCutoff = fs.SizeSuffix(200 * 1024 * 1024)
+	defaultUploadCutoff = fs.SizeSuffix(5 * 1024 * 1024) // as per https://docs.drime.cloud/uploads-guide
 )
 
 // Register with Fs