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/next.config.mjs

@@ -1,5 +1,7 @@
 import mdx from "@next/mdx"
 import bundleAnalyzer from "@next/bundle-analyzer"
+import rehypeMdxCodeProps from "rehype-mdx-code-props"
+import rehypeSlug from "rehype-slug"
 
 /** @type {import('next').NextConfig} */
 const nextConfig = {
@@ -15,7 +17,15 @@ const nextConfig = {
 const withMDX = mdx({
   extension: /\.mdx?$/,
   options: {
-    rehypePlugins: [],
+    rehypePlugins: [
+      [
+        rehypeMdxCodeProps,
+        {
+          tagName: "code",
+        },
+      ],
+      [rehypeSlug],
+    ],
     development: process.env.NODE_ENV === "development",
   },
 })