docs: improvements to API reference intro sections (#9397)

- Improve intro sections of API reference to utilize divided columns
- Improve the content of the intro sections
- Add a new Workflows section to explain the workflows badge and how to use it
- Fixes to headings and add anchor for copying the link to a section
- Fixes responsiveness of intro sections on mobile devices
- Other: fix loading not showing when a sidebar category is opened.

Closes DOCS-932, DOCS-934, DOCS-937

Preview: https://api-reference-v2-git-docs-api-ref-intro-fixes-medusajs.vercel.app/v2/api/store

www/apps/api-reference/package.json

@@ -45,6 +45,8 @@
     "react-intersection-observer": "^9.5.3",
     "react-tooltip": "^5.19.0",
     "react-transition-group": "^4.4.5",
+    "rehype-mdx-code-props": "^2.0.0",
+    "rehype-slug": "^6.0.0",
     "slugify": "^1.6.6",
     "swr": "^2.2.0",
     "tailwind": "*",