Re-add docs page tabs

[kylegach]

How to test

To see the docs page tabs, the content had to be updated. Therefore, a demo PR was created for testing.

You will not be able to test in this PR's deploy preview.

1. You should see functional page-level tabs on this page (which is built from these content changes):

   https://deploy-preview-260--storybook-frontpage.netlify.app/docs/8.6/api/csf

   Confirm that the other tab's URL is /docs/8.6/api/csf/csf-factories. The actual content there is WIP and not relevant to this PR.

2. And you should not see them on this page:

   https://deploy-preview-260--storybook-frontpage.netlify.app/docs/api/csf

[netlify]

✅ Deploy Preview for storybook-frontpage ready!

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🔨 Latest commit	401e347
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[netlify]

✅ Deploy Preview for storybook-addon-catalog ready!

Name	Link
🔨 Latest commit	401e347
🔍 Latest deploy log	https://app.netlify.com/sites/storybook-addon-catalog/deploys/679a3ead58c93b0008b4aa2c
😎 Deploy Preview	https://deploy-preview-259--storybook-addon-catalog.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

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[winkerVSbecks]

@kylegach https://deploy-preview-260--storybook-frontpage.netlify.app/docs/api/csf seems to error out

[winkerVSbecks]

Not sure what is causing the deploy to error out but otherwise good to merge

[kylegach]

deploy-preview-260--storybook-frontpage.netlify.app/docs/api/csf seems to error out

Strange. It works in a local build and in the redeploy I just did, so I'm going to consider that a fluke.

Thanks for the review!