fine-tune apidocs markup for dark mode

[xrstf]

This is the result of working a bit more on the dark mode for the apidocs. I had to extend the markup a bit, now at least the result is now pretty:

I adopted the font that is used on kubernetes.io, plus the colors in light mode were adjusted a bit to better match the Kubernetes website.

The markup is now also setup for an CSS-only automatic dark mode, which avoids the previous flash-of-white before the JS kicked in and applied the theme-dark class.

I also renamed the scroll-apiref.js, since the file is not just responsible for the scrolling behaviour, but also the dark mode toggler. I hope this won't cause issues when the website repo PR is eventually merged.

[tengqm]

Thanks. /lgtm /approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: tengqm, xrstf

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[xrstf]

@tengqm Thanks a lot for your super quick reviews on all these PRs, it's really appreciated :-) Is there anything else I need to do to complete this? The markup on https://kubernetes.io/docs/reference/generated/kubernetes-api/v1.27/ is still the old one, but the new CSS/JS is already live.

[tengqm]

@xrstf I've sent a PR refreshing the HTML (https://github.com/kubernetes/website/pull/43139) and it has been merged.