[docs-infra] Refine how subheaders are shown in the page body

[danilo-leal]

Summary

What I mean by this issue is easier understood from just seeing the mock-up below:

Current	New design

Very often, throughout the products, we add the subheader word as part of a page title, which makes sense to give readers context. However, I feel like the design above is a much cleaner way of displaying that, particularly because we don't need the category word/name to be so big, and having the hyphen + spacing looks a bit clunky. This shouldn't change the page title, though, as in what we see in the browser's tab—in there, I think it's fine to have "Subheader - Title" still.

I'll leave myself assigned to this for the design part, but I'll need engineering help to figure out how to architect this via potentially the pages.ts file setup (or something else, entirely!) 😬

Search keywords: subheaders design display