(cherry-pick) Add new "Get started" document (#2700)

[ADubhlaoich]

This commit adds a new "Get started" document for NGINX Gateway Fabric. It re-orders the top level page so that it is second after "Overview" as a means to get a reader started as quickly as possible, and is a combination of the existing kind guide, a Helm installation path and the cafe-example on GitHub.

As part of this work, the original kind guide has been deleted: the only context lost is regarding port forwarding, which this new document mentions not requiring. The README for the cafe-example could also be stripped down as a result: the step "skipped" regards how to use a different hostname.

Both of these could instead be added to a general network configuration document.

Proposed changes

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Closes #ISSUE

Checklist

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• 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

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.12%. Comparing base (32a9d42) to head (4c1ef58).
Report is 1 commits behind head on release-1.4.

Additional details and impacted files

@@               Coverage Diff               @@
##           release-1.4    #2717      +/-   ##
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+ Coverage        88.84%   89.12%   +0.28%     
===============================================
  Files              100      100              
  Lines             7527     9554    +2027     
  Branches            50       50              
===============================================
+ Hits              6687     8515    +1828     
- Misses             784      983     +199     
  Partials            56       56              

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