Feat: Dual-stack v4/v6 support

[yorickdowne]

Is your feature request related to a problem? Please describe.

Home stakers increasingly find themselves behind CGNAT, which makes it impossible to open incoming P2P ports on IPv4.

Describe the solution you'd like

Implement dual-stack v4/v6 in the ssv node. Opt-in to begin, and default once we have some experience. This would make the tcp and udp ports available on both v4 and v6. Ports should be the same in either protocol by default.

Describe alternatives you've considered

Users can ask their ISP to disable CGNAT. This is not always trivial - it may not be available at all or require a "business plan"

Additional context

Please see https://ipv6eth.info for tracking of CL and EL clients' dual-stack abilities. Sonic, myself and Ethstaker are on a dual-stack push to make life better for home stakers everywhere.