feat: Update NGINX Ingress Controller links for consistency

[ADubhlaoich]

Proposed changes

This commit updates all non-uniform NGINX Ingress Controller links to follow the standardised Hugo ref convention. This involves updating the paths of every existing ref to add the /nic/ subfolder, excising any remaining relref uses and removing Markdown-style inline links.

Outside of style uniformity, it means that broken links will now be detected by Hugo's built-in error mechanisms, making it easier to maintain link integrity. Many affected files also had small metadata or formatting changes applied to them.

Checklist

Before merging a pull request, run through this checklist and mark each as complete.

• I have read the contributing guidelines
• I have signed the F5 Contributor License Agreement (CLA)
• I have rebased my branch onto main
• I have ensured my PR is targeting the main branch and pulling from my branch from my own fork
• I have ensured that the commit messages adhere to Conventional Commits
• I have ensured that documentation content adheres to the style guide
• If the change involves potentially sensitive changes¹, I have assessed the possible impact
• If applicable, I have added tests that prove my fix is effective or that my feature works
• I have ensured that existing tests pass after adding my changes
• If applicable, I have updated README.md and CHANGELOG.md

Footnotes

1. Potentially sensitive changes include anything involving code, personally identify information (PII), live URLs or significant amounts of new or revised documentation. Please refer to our style guide for guidance about placeholder content. ↩

[github-actions]

✅ Deploy Preview will be available once build job completes!

Name	Link
😎 Deploy Preview	https://frontdoor-test-docs.nginx.com/previews/docs/713/

---

[javorszky]

Checked out branch, spun up a local copy with make watch, double checked that the links indeed go to the same local of the docs, and that the images are correctly linked and appear.

Besides the one page I can't find being linked from anywhere, it's good to go