dns-manager: always apply options from [global-dns]

Attempt to configure global resolv.conf options with a configuration file,

  [global-dns]
  options=timeout:1

or via D-Bus API,

  # busctl set-property org.freedesktop.NetworkManager \
      /org/freedesktop/NetworkManager org.freedesktop.NetworkManager \
      GlobalDnsConfiguration 'a{sv}' 2 \
          "options" as 1 "timeout:1" \
          "domains" a{sv} 0

results in an error:

  Nov 24 13:15:21 c8t.local NetworkManager[501184]: <debug> [1669292121.3904]
      manager: set global DNS failed with error: Global
      DNS configuration is missing the default domain

This appears to be an artifical limitation. Lift it.

https://bugzilla.redhat.com/show_bug.cgi?id=2019306