Social media previews

[liliakai]

Tracking issue for Kai to look into og:image tags on our pages. They don't seem to be working as expected re: gitbook docs and may need to follow up with their support forum.

[liliakai]

Notes to self:

Gitbook AI says it should be possible to set previews for pages, but the docs say it's only for site sections which is a feature we don't have access too.

Docs also says that if we disable the global site social media preview, then individual pages should get previews automagically generated from their content. Need to test this a bit more as it did not seem to be happening on my personal docs site, but my theory is the preview is generated with some delay after the first time they are requested. Will try again in 24 hrs.