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/users-sources/sources/social-logins/plex/index.md

@@ -1,9 +1,8 @@
 ---
 title: Plex
+support_level: community
 ---
 
-<span class="badge badge--secondary">Support level: Community</span>
-
 Allows users to authenticate using their Plex credentials
 
 ## Preparation