workercmd: support dns proxy in containerd
workercmd: support dns proxy in containerd

given that topgun/k8s already tests all of the possible scenarios
involving configuring DNS servers, we rely on that suite for ensuring
that this is properly done.

see https://github.com/concourse/concourse/blob/fab3de1722a2ce998d3710bd066453594f24ec57/topgun/k8s/dns_proxy_test.go

Signed-off-by: Ciro S. Costa <4f5054ab2db051d03adf9068233a850c82b24437@pivotal.io>
Co-authored-by: Muntasir Chowdhury <3af480f42ae632f8ec7bb4ce9ac5df283cd495d6@pivotal.io>

concourse/concourse,concourse/concourse,concourse/concourse,concourse/concourse,concourse/concourse