[cern] Make dual_stack an opt-out feature
- add ip_family_policy which defaults to dual_stack
- expose portal_network6_cidr,pods_network6_cidr as a labels keeping the same default cidr
- drop EndpointSlice, IPv6DualStack which are True anyway since 1.18 and 1.21 respectively
closes https://gitlab.cern.ch/kubernetes/project/-/issues/300
Signed-off-by: Spyros Trigazis spyridon.trigazis@cern.ch