fix: add more optimizations to putMetacacheObject() (#12916)

- avoid extra lookup for 'xl.meta' since we are
  definitely sure that it doesn't exist.

- use this in newMultipartUpload() as well

- also additionally do not write with O_DSYNC
  to avoid loading the drives, instead create
  'xl.meta' for listing operations without
  O_DSYNC since these are ephemeral objects.

- do the same with newMultipartUpload() since
  it gets synced when the PutObjectPart() is
  attempted, we do not need to tax newMultipartUpload()
  instead.

cmd/storage-datatypes.go

@@ -179,6 +179,8 @@ type FileInfo struct {
 
 	NumVersions      int
 	SuccessorModTime time.Time
+
+	Fresh bool // indicates this is a first time call to write FileInfo.
 }
 
 // InlineData returns true if object contents are inlined alongside its metadata.