feat: Migrate NGINX Gateway Fabric documentation into repository

[ADubhlaoich]

Proposed changes

With the newly open source documentation repository, we can now consolidate all NGINX documentation into one place. This has a lots of benefits which include but are not limited to more effective content re-use, pipeline engineering and style enforcement.

This pull request adds all of the content for NGINX Gateway Fabric, and updates all relevant folder and file names, including link references. Once this content has been successfully deployed, a PR to remove all documentation traces and tooling will be opened in the Gateway Fabric repository, decoupling the documentation fully.

It also updates the frontmatter of every single page in the documentation set. They are now all consistent in their fields and formatting, and a handful of IA or heading changes have been made as low-hanging fruit to bring the documentation set closer to full consistency.

Checklist

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

• I have signed the F5 Contributor License Agreement (CLA)

• I have read the contributing guidelines

• If applicable, I have added tests that prove my fix is effective or that my feature works

• If applicable, I have checked that any relevant tests pass after adding my changes

• I have updated any relevant documentation (README.md and CHANGELOG.md)

• 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

• If the change involves:

  • Code
  • Anything that resembles Personally identifying information (PII)
    • Make sure to use placeholders such as <username> in place of PII
  • URLs (watch for typosquatting)
  • Significant new/revised content

  In these cases, the change will require at least two (2) approvals before merging

[ADubhlaoich]

The main effort for this PR has actually been completed, and it runs locally as expected right now.

I'm keeping this in draft for the time being as I want to fix up the frontmatter metadata for the entire documentation set while I have it in front of me.

[github-actions]

✅ Deploy Preview will be available once build job completes!

Name	Link
😎 Deploy Preview	https://frontdoor-test-docs.nginx.com/previews/docs/81/

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[ADubhlaoich]

Opened the PR up, and updated the original message: I have updated the frontmatter for all but one file.

[ADubhlaoich]

Created a paired PR for NGINX Gateway Fabric to remove the documentation from their repository once this has been merged.

nginx/nginx-gateway-fabric#3047

There is also a pending PR for the deployment configuration changes necessary once this has been merged.