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/components/Section/index.tsx

@@ -19,6 +19,7 @@ const Section = ({
     rootElm: sectionRef.current || undefined,
     enable: checkActiveOnScroll,
     useDefaultIfNoActive: false,
+    maxLevel: 2,
   })
   const { setActivePath } = useSidebar()
   const router = useRouter()