Convert several pages to leaf bundles with WebP screenshots, add
api-keys, domain-availability, notifications, provider-features,
quotas, services, settings, signup and subdomains pages, and refresh
existing content.
Enable Goldmark block-level attributes so the relearn `children`
shortcode applies its CSS classes instead of printing them literally
in the table-of-contents pages. Also expand the deploy, plugins,
records, and email reference docs and add the checks pages.
