Add custom landing page to N1 via index.md

[lamATnginx]

Proposed changes

Closes https://github.com/nginxinc/docs-platform/issues/519

Checklist

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Footnotes

1. Potentially sensitive changes include anything involving code, personally identify information (PII), live URLs or significant amounts of new or revised documentation. Please refer to our style guide for guidance about placeholder content. ↩

[mjang]

I like the approach. We do need to test this, aka, see what happens after we:

• Implement the card* plugin
• Remove the list-main.html file

[danielledeleo]

Can you add a screenshot?

[nginx-jack]

Do we want to set showAsCards="true" here?