refactor: use mdx for content

- less dependencies
- no need for gray-matter
- no need for extra utils and interactions with filesystem

next.config.js

@@ -1,3 +1,16 @@
+const withMDX = require("@next/mdx")({
+  extension: /\.mdx?$/,
+  options: {
+    // If you use remark-gfm, you'll need to use next.config.mjs
+    // as the package is ESM only
+    // https://github.com/remarkjs/remark-gfm#install
+    remarkPlugins: [],
+    rehypePlugins: [],
+    // If you use `MDXProvider`, uncomment the following line.
+    // providerImportSource: "@mdx-js/react",
+  },
+});
+
 /** @type {import('next').NextConfig} */
 const nextConfig = {
   reactStrictMode: true,
@@ -5,7 +18,8 @@ const nextConfig = {
   experimental: {
     newNextLinkBehavior: true,
     scrollRestoration: true,
-  }
-}
+  },
+  pageExtensions: ["js", "jsx", "ts", "tsx", "md", "mdx"],
+};
 
-module.exports = nextConfig;
+module.exports = withMDX(nextConfig);