IPv6 support in Quay image

Goal: Native IPv6 support for all components that make up the Red Hat Quay product.

Background: Quay should be agnostic of IPv6 or IPv4 for the most part but several components might need adjustments or additional / different configuration examples. We mainly need testing here to find out if something breaks in an environment where only IPv6 is used. For example: Quay's container uses nginx to handle initial requests from external clients. We should determine whether ipv6 is currently implemented and document accordingly, or modify the nginx configuration(s) to allow ipv6 to be used.

Why is this important: Native IPv6 is coming up more often in Telco and Edge environments. While Quay still has to find its way into these restricted environments there are use cases today where it serves a central registry in some form of hub cluster. Unlike other IPv6 environments today where there is also IPv4 present, in these scenarios a pure-play IPv6 implementation is desired.

Deliverables:

• Red Hat Quay officially supports IPv6
• The operator can deploy Quay in IPv4/IPv6 dual-stack OCP clusters where Quay uses IPv6
• Any documentation that's required

Out of scope:

• Quay.io supporting IPv6 (this is likely very straight forward and mainly a matter of adjusting our nginx config and several AWS ingress-related services)