Update design for Status Page

[MattIPv4]

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👋 Given the incident today, it seems folks have remembered that we have a status page (though it is very rarely used luckily). It'd be good to get the design updated on it to match the theme used on the site where possible.

Status page gives us very limited control, allowing for custom SCSS to be defined that'll apply globally to all pages and the ability to inject custom HTML (and JavaScript) in the footer of all pages.

The current customisations are documented in nodejs/build#2299. Either we get that PR updated to capture new changes, or perhaps documenting those would be better in this repository now.