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/yarn.lock

@@ -5582,6 +5582,8 @@ __metadata:
     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: "*"