Add Routing Traffic to Your Application Guide

[kate-osborn]

Proposed changes

Problem: As a potential user of NKG, I want a guide to help me understand how to host an application API with NKG so that I can easily understand how to start using NKG in my environment immediately.

Solution: Add a use case guide that describes how to route all traffic to a single application running in Kubernetes using NKG.

Testing: Ran through guide

This is meant to be the basic use case guide so we are intentionally not introducing every field and variation of the Gateway API. We want to give the users enough information to get started. Other use case guides will build on the information provided in this guide.

Closes #876

The diagrams are written using mermaid, but the GitHub mermaid integration is not working well with dark mode, so I added them as pngs. The mermaid source files are in the /docs/images/source directory. This will allow internal and external contributors to easily modify the diagrams.

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

[mpstefan]

Paired with Kate on this. Added comments to other input.

[ciarams87]

LGTM! 🎉

[pleshakov]

👍

[ADubhlaoich]

LGTM, just two small suggestions.