docs: Set up updated list-main for N1C

[mjang]

Proposed changes

As part of the release of the updated NGINX One Console front page, I used layouts/partials/list-main.html in the github.com/nginx/documentation repository.

Since that file now belongs in this nginx-hugo-theme repository, I'm setting up this PR here.

Future: as we start supporting NGINX One Console monitoring of other NGINX products, we'll delete those products from the "Other Products" section.

Closes #271

Checklist

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

• I have read the CONTRIBUTING document
• 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)

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[github-actions]

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[mjang]

Note, once this is approved / merged, I'll follow up with a PR to remove the same file from https://github.com/nginx/documentation.

[lamATnginx]

Duplicate of #273