instance: add support for multiple instance IPs

[BeryJu]

closes #525

[netlify]

✅ Deploy Preview for beryju-gravity canceled.

Name	Link
🔨 Latest commit	c0477a3
🔍 Latest deploy log	https://app.netlify.com/projects/beryju-gravity/deploys/69ff46df05ca3d0008096185

[codecov]

Codecov Report

❌ Patch coverage is 80.00000% with 19 lines in your changes missing coverage. Please review.
✅ Project coverage is 69.52%. Comparing base (139a61c) to head (c0477a3).
⚠️ Report is 1 commits behind head on main.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
pkg/roles/dhcp/role.go	69.23%	6 Missing and 6 partials ⚠️
pkg/roles/dhcp/dhcp_request4.go	42.85%	4 Missing ⚠️
pkg/extconfig/config.go	84.61%	1 Missing and 1 partial ⚠️
pkg/roles/dns/role.go	92.30%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2205      +/-   ##
==========================================
+ Coverage   69.45%   69.52%   +0.06%     
==========================================
  Files         140      140              
  Lines        7645     7655      +10     
==========================================
+ Hits         5310     5322      +12     
+ Misses       1797     1793       -4     
- Partials      538      540       +2     

Flag	Coverage Δ
bench	12.39% <27.36%> (+0.24%)	⬆️
e2e	45.16% <65.26%> (-0.01%)	⬇️
unittest	55.29% <69.47%> (-0.14%)	⬇️

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[github-actions]

Docker Images

This PR has been built and pushed to the container registry.

Standard image:

docker pull ghcr.io/beryju/gravity:pr-2205

Debug image:

docker pull ghcr.io/beryju/gravity:pr-2205-debug