feat(cli,packagemanager): implemented first working windows and macos versions

in order to implement sst for windows and macos the structure of
osmanager has been changed.
Now osmanager has a new field pm, which contains the specific
packagemanager for the os.
Linux packagemanagers have been implemented as packagemanagers on their
own.

packagemanager/win_dummy.go

@@ -0,0 +1,8 @@
+//go:build linux
+// +build linux
+
+package packagemanager
+
+func platformInfoWin() (*OS, error) {
+	return nil, nil
+}