Support windows metadata using generic attribs

Add new generic_attributes attribute in Node.
Use the generic attributes to add support for creation time and file attributes like hidden, readonly, encrypted in windows. Handle permission errors for readonly files in windows.
Handle backup and restore of encrypted attributes using windows system calls.

internal/restorer/fileswriter.go

@@ -50,16 +50,26 @@ func (w *filesWriter) writeToFile(path string, blob []byte, offset int64, create
 			bucket.files[path].users++
 			return wr, nil
 		}
-
-		var flags int
+		var f *os.File
+		var err error
 		if createSize >= 0 {
-			flags = os.O_CREATE | os.O_TRUNC | os.O_WRONLY
-		} else {
-			flags = os.O_WRONLY
-		}
-
-		f, err := os.OpenFile(path, flags, 0600)
-		if err != nil {
+			if f, err = os.OpenFile(path, os.O_CREATE|os.O_TRUNC|os.O_WRONLY, 0600); err != nil {
+				if fs.IsAccessDenied(err) {
+					// If file is readonly, clear the readonly flag by resetting the
+					// permissions of the file and try again
+					// as the metadata will be set again in the second pass and the
+					// readonly flag will be applied again if needed.
+					if err = fs.ResetPermissions(path); err != nil {
+						return nil, err
+					}
+					if f, err = os.OpenFile(path, os.O_TRUNC|os.O_WRONLY, 0600); err != nil {
+						return nil, err
+					}
+				} else {
+					return nil, err
+				}
+			}
+		} else if f, err = os.OpenFile(path, os.O_WRONLY, 0600); err != nil {
 			return nil, err
 		}