(cherrypick) feat: Update docs configuration for new logo (#2867)

[ADubhlaoich]

Proposed changes

In a prior commit, the Hugo theme for the documentation was updated. With that update, the new logo for NGINX Gateway Fabric was made available (Previously used for Service Mesh).

This commit makes the necessary configuration changes for the new logo to be available: there is a paired pull request for the main documentation website.

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.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.86%. Comparing base (a890a8b) to head (10a114e).
Report is 1 commits behind head on release-1.5.

Additional details and impacted files

@@             Coverage Diff              @@
##           release-1.5    #2880   +/-   ##
============================================
  Coverage        89.86%   89.86%           
============================================
  Files              107      107           
  Lines            10997    10997           
  Branches            50       50           
============================================
  Hits              9883     9883           
  Misses            1054     1054           
  Partials            60       60           

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