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/MDXComponents/H2/index.tsx

@@ -1,6 +1,6 @@
 "use client"
 
-import { useScrollController, useSidebar } from "docs-ui"
+import { useScrollController, useSidebar, H2 as UiH2 } from "docs-ui"
 import { useEffect, useMemo, useRef, useState } from "react"
 import getSectionId from "../../../utils/get-section-id"
 
@@ -39,9 +39,9 @@ const H2 = ({ children, ...props }: H2Props) => {
   }, [id])
 
   return (
-    <h2 {...props} id={id} ref={headingRef}>
+    <UiH2 {...props} id={id} passRef={headingRef}>
       {children}
-    </h2>
+    </UiH2>
   )
 }