oci: Add WithDomainname

A domainname field was recently added to the OCI spec. Prior to this
folks would need to set this with a sysctl, but now runtimes should be
able to setdomainname(2). There's an open change to runc at the moment
to add support for this so I've just left testing as a couple spec
validations in CRI until that's in and usable.

Signed-off-by: Danny Canter <danny@dcantah.dev>

oci/spec_opts.go

@@ -274,6 +274,14 @@ func WithHostname(name string) SpecOpts {
 	}
 }
 
+// WithDomainname sets the container's NIS domain name
+func WithDomainname(name string) SpecOpts {
+	return func(_ context.Context, _ Client, _ *containers.Container, s *Spec) error {
+		s.Domainname = name
+		return nil
+	}
+}
+
 // WithMounts appends mounts
 func WithMounts(mounts []specs.Mount) SpecOpts {
 	return func(_ context.Context, _ Client, _ *containers.Container, s *Spec) error {