website: Use Docusaurus Frontmatter for badges (#12893)

website/docs: Reduce redundant usage of badges. Move badge logic to components.

- Fix JSX class name warning.
- Remove duplicate titles.
- Flesh out `support_level` frontmatter.

website/docs/add-secure-apps/providers/proxy/_nginx_standalone.md

@@ -1,4 +1,4 @@
-```
+```nginx
 # Upgrade WebSocket if requested, otherwise use keepalive
 map $http_upgrade $connection_upgrade_keepalive {
     default upgrade;