chore: Use F5 artifactory GOPROXY and self-hosted runners

[ciarams87]

Proposed changes

Use GOPROXY to F5 artifactory for dependencies (excluding forks) and self-hosted runners for building production artifacts

Testing: See https://github.com/nginx/nginx-gateway-fabric/actions/runs/16832379405 for a test workflow.

NB: This PR must remain in DRAFT for now

Checklist

Before creating a PR, run through this checklist and mark each as complete.

• I have read the CONTRIBUTING doc
• I have added tests that prove my fix is effective or that my feature works
• I have checked that all unit tests pass after adding my changes
• I have updated necessary documentation
• I have rebased my branch onto main
• I will ensure my PR is targeting the main branch and pulling from my branch from my own fork

Release notes

If this PR introduces a change that affects users and needs to be mentioned in the release notes,
please add a brief note that summarizes the change.

NONE

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.16%. Comparing base (6c410e5) to head (5e0b317).
⚠️ Report is 5 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3710      +/-   ##
==========================================
- Coverage   87.17%   87.16%   -0.01%     
==========================================
  Files         128      128              
  Lines       15779    15779              
  Branches       62       62              
==========================================
- Hits        13755    13754       -1     
- Misses       1865     1866       +1     
  Partials      159      159              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.