message: tmpfiles: add runtime config directory
  This adds `/run/zincati/config.d`, which stores runtime/volatile
  configuration fragments.
diff: #Type Path Mode User Group Age Argument
  d /run/zincati 0775 zincati zincati - -
  +# Runtime configuration fragments
  +d /run/zincati/config.d 0775 zincati zincati - -
  +
  # Runtime state, unstable/private implementation details
  d /run/zincati/private 0770 zincati zincati - -
  