Added new shortcodes + partials to support custom landing page

[lamATnginx]

Proposed changes

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

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)

[github-actions]

✅ Deploy Preview will be available once build job completes!

Name	Link
😎 Deploy Preview	https://frontdoor-test-docs.nginx.com/previews/nginx-hugo-theme/273/

---

[danielledeleo]

• add example site usage
• prevent inner shortcodes from being used in other contexts
• add an optional class option to card-layout to setup a grid layout with cards with borders, like the home page
• in the default list view, remove side padding
• adjust font weights