Default the document editor demo on the website to be expanded

[emmatown]

The whole point of the page is to demo the editor so having it collapsed by default seems weird. Also removed a duplicate border.

(No changeset for the change to fields-document because it doesn't change anything that's visible externally)

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Name	Status	Preview	Updated
keystone-next-docs	✅ Ready (Inspect)	Visit Preview	Oct 21, 2022 at 0:24AM (UTC)

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