docs[patch]: Make Docusaurus and Vercel add trailing slashes when navigating by default (#20014)

Should hopefully avoid weird broken link edge cases.

Relative links now trip up the Docusaurus broken link checker, so this
PR also removes them.

Also snuck in a small addition about asyncio

docs/docusaurus.config.js

@@ -19,7 +19,7 @@ const config = {
   // Set the /<baseUrl>/ pathname under which your site is served
   // For GitHub pages deployment, it is often '/<projectName>/'
   baseUrl: "/",
-
+  trailingSlash: true,
   onBrokenLinks: "throw",
   onBrokenMarkdownLinks: "throw",