fix symlink issue on windows for goctl (#1034)

* fix symlink issue on windows for goctl

* move readlink into separate file

tools/goctl/util/readlink+polyfill.go

@@ -0,0 +1,8 @@
+//go:build windows
+// +build windows
+
+package util
+
+func ReadLink(name string) (string, error) {
+	return name, nil
+}