Fix externalhosts to advertise both IPv4 and IPv6 addresses

[wearedood]

Fixes #8801

When a domain resolves to both IPv4 and IPv6 addresses, the node should advertise both protocols. Previously, only one address was returned due to using ResolveTCPAddr which returns a single address.

This change:

• Uses net.LookupHost to get all IP addresses for a domain
• Creates addresses for each IP found (both IPv4 and IPv6)
• Handles errors gracefully by continuing with other IPs if one fails
• Returns error if no valid addresses are found
• Updates function signature to return []net.Addr instead of single net.Addr

Change Description

Description of change / link to associated issue.

Steps to Test

Steps for reviewers to follow to test the change.

Pull Request Checklist

Testing

• [ ] Your PR passes all CI checks.
• [ ] Tests covering the positive and negative (error paths) are included.
• [ ] Bug fixes contain tests triggering the bug to prevent regressions.

Code Style and Documentation

• [ ] The change is not insubstantial. Typo fixes are not accepted to fight bot spam.
• [ ] The change obeys the Code Documentation and Commenting guidelines, and lines wrap at 80.
• [ ] Commits follow the Ideal Git Commit Structure.
• [ ] Any new logging statements use an appropriate subsystem and logging level.
• [ ] Any new lncli commands have appropriate tags in the comments for the rpc in the proto file.
• [ ] There is a change description in the release notes, or [skip ci] in the commit message for small changes.

📝 Please see our Contribution Guidelines for further guidance.

[lightninglabs-deploy]

@wearedood, remember to re-request review from reviewers when ready