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.

cmd/restic/cmd_find.go

@@ -126,6 +126,7 @@ func (s *statefulOutput) PrintPatternJSON(path string, node *restic.Node) {
 		// Make the following attributes disappear
 		Name               byte `json:"name,omitempty"`
 		ExtendedAttributes byte `json:"extended_attributes,omitempty"`
+		GenericAttributes  byte `json:"generic_attributes,omitempty"`
 		Device             byte `json:"device,omitempty"`
 		Content            byte `json:"content,omitempty"`
 		Subtree            byte `json:"subtree,omitempty"`