feat(tmpfiles) add some more /etc symlinks

Support was added for the following symlinks:
  /etc/os-release   ->  /usr/share/baselayout/os-release
  /etc/lsb-release  ->  /usr/share/baselayout/lsb-release
  /etc/machine-id   ->  /usr/share/baselayout/machine-id

Other packages create these files, but if they get removed from the
system, they will be properly re-created now by the systemd-tmpfiles
program.