MicroShift IPV6 support

Feature Overview (aka. Goal Summary)  

Test and validate MicroShift is working correctly in IPV6 environments.

Goals (aka. expected user outcomes)

1. Dualstack: Users can run MicroShift and their workload in IP V4/V6 dual stack environments, meaning ingress and egress traffic can be on V4 or V6 traffic, even mixed and parallel.
2. Single-V6 stack: User can run MicroShift and their workload in pure IPV6 only environments.

Requirements (aka. Acceptance Criteria):

1. Both V4 and V6 CIDR for cluster/pod and service networks need to be configurable. 
2. Ingress Controller needs to handle V6 traffic correctly
3. Egress needs to be fully functional, e.g. a pod can connect to a V6 IP Adress (e.g. from DNS) seamlessley.
4. Support of migration/upgrade from single stack V4 to dual stack V4+V6 should be supported. MicroShift restart or whole system reboot on that change is acceptable. Converting back from dualstack to V4 only is NOT supported. This migration/upgrade requirement is a stretch goal: Its not mandatory on initial release of the feature and can be added / split into a later release if needed. 

Questions to Answer (Optional):

none

Out of Scope

1. Converting clusters back from dualstack V4+V6 config back to single stack V4 only is out of scope. The other direction single stack V4 to multi-stack V4+V6 is a stretch goal (see requirements)
2. MultiNode via IPV6 - MicroShift uses multi node currently only for CNCF certification, which does not require IPV6. So adding a worker node to MicroShift via IPV6 is out of scope of this feature. 

Background

We see more and more adaption of IP V6, hence we have to ensure MicroShift is ready for this.

Customer Considerations

none

Documentation Considerations

MicroShift networking documentation needs to be augmented by examples on how to config dualstack V4V6 and singlestack V6 only.

Interoperability Considerations

1. ovn-k: This relies on ovn-k implementation from OpenShift, but no special integration / testing expected.
2. mmgt solutions:  No special considerations/feature required. AAP and ACM also support dual stack / single stack. As long as communication in the required direction can be establish, it simply works. Examples AAP requires ssh from hub to edge, ACM requires  https edge to hub both directions).  Of course there are combinations where communication is not possible due to IP limitations (e.g. AAP on V4 only, edge on V6 only: AAP cant connect to edge). But that is elementary network infra requirements and out of scope of this feature.