Test and document IPv6 compatible configuration

As IPv6 adoption continues to grow, we need to test and validate Omnibus GitLab in IPv6 environments. We've encountered IPv6-related issues previously, though their might not be relevant anymore:

• yaml.parser.ParserError error when configuring ... (#9374)
• IPv4 or IPv6 localhost standardization (#5449)
• Poor IPv6 support for nginx['listen_addresses'] (#1253)
• nginx only listens to IPv4 (#673)
• `chef-zero` binds to `::1` even if you disable ... (#576)

The Omnibus default configuration won't work on IPv6 single stacks environments. For example Puma listens on IPv4 by default.

Acceptance Criteria

We should test deploying Omnibus (HA) in a IPv6 single stack environment, document the necessary configuration, and create follow-up for issues we identified.

• Omnibus HA in IPv6 single stack environment deployed
• Configuration and gaps documented
• Follow-up created
• Outdated IPv6 issues closed