[Request]: full RFC-compliant IPv6

### Feature or enhancement request details

As containers are their own VMs, you'd expect they behave as any other RFC-compliant Linux machine, i.e.:
- receive Router Assignments [RFC 4862](https://www.rfc-editor.org/rfc/rfc4862)
- receive RDNSS [RFC 8106](https://www.rfc-editor.org/rfc/rfc8106)
- generate 1 opaque stable SLAAC address [RFC 7217](https://datatracker.ietf.org/doc/rfc7217/)
- generate 1 SLAAC privacy address [RFC 4941](https://datatracker.ietf.org/doc/html/rfc4941)
- generate a link-local address [RFC 4291](https://www.rfc-editor.org/rfc/rfc4291)
- use PREF64 if advertised [RFC 8781](https://www.rfc-editor.org/rfc/rfc8781)
- SLAAC is mandatory, DHCPv6 is optional, so maybe not high priority, but still [RFC8415](https://www.rfc-editor.org/rfc/rfc8415)

Manual configuration of IPv6 should really be a last-resort fallback, not the default.

Is there a roadmap for this?

### Code of Conduct

- [x] I agree to follow this project's Code of Conduct

No files, tests, or entry points are named. Start by locating the container networking entry point and reviewing how IPv6 configuration is currently handled. Done means supporting the requested RFC behaviors, including router assignments, RDNSS, SLAAC addresses, link-local addressing, PREF64, and optional DHCPv6.

Written by the indexing model from the issue text.