feat: add DHCPv6 support and enhance documentation for dual-stack configuration

[alexlovelltroy]

Description

This pull request adds comprehensive support for DHCPv6 and IPv6 DNS records to the CoreSMD plugins for both CoreDHCP and CoreDNS. The changes include updates to documentation, example configuration files, and plugin implementation to enable dual-stack (IPv4 and IPv6) networking. The CoreDHCP plugin (coresmd) now supports DHCPv6 address assignment, hostname configuration, and iPXE boot options, while the CoreDNS plugin can resolve AAAA records and perform IPv6 reverse lookups.

DHCPv6 and IPv6 support for CoreDHCP:

• The coresmd plugin for CoreDHCP now supports DHCPv6, including IPv6 address assignment from SMD, FQDN option handling, and iPXE boot configuration. The implementation includes a new Handler6 function and updated setup logic to parse configuration and interact with SMD for IPv6 leases. [1] [2]
• Example configuration files (coredhcp.yaml and coredhcp-minimal.yaml) and documentation have been updated to show dual-stack (DHCPv4 and DHCPv6) setups and explain configuration options specific to IPv6. [1] [2] [3]

IPv6 support for CoreDNS:

• The CoreDNS plugin documentation and handler logic have been updated to clarify support for AAAA records and IPv6 PTR lookups, with examples for both forward and reverse DNS resolution. [1] [2] [3] [4] [5] [6]

Documentation improvements:

• README files for both CoreDHCP and CoreDNS have been revised to explicitly state support for DHCPv6 and IPv6 DNS records, with updated feature lists and configuration examples. [1] [2]

Testing and validation:

• The CoreDHCP plugin test suite has been updated to verify that DHCPv6 setup is now supported and configuration validation works as expected.

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References:
[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14]

Checklist

• I have added/updated comments where needed
• I have added tests that prove my fix is effective or my feature works
• I have run make test (or equivalent) locally and all tests pass
• DCO Sign-off: All commits are signed off (git commit -s) with my real name and email

Fixes #40

Type of Change

• Bug fix
• New feature
• Breaking change
• Documentation update

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For more info, see Contributing Guidelines.

[alexlovelltroy]

@sujit-jadhav Can you try with this? the PR autobuilt a a container at ghcr.io/openchami/coresmd:pr-41-amd64

[synackd]

LGTM on code review. Once we get a successful test confirmation, this can be merged.

[sujit-jadhav]

@alexlovelltroy I am on it. I have tested the container on the OIM and it is working fine, I am setting the IPv6 environment at switch level, will check if nodes are booting, we are good to go.