refactor: use mdx for content

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

package.json

@@ -13,14 +13,14 @@
   },
   "dependencies": {
     "@headlessui/react": "^1.7.4",
+    "@mdx-js/loader": "^2.2.1",
+    "@mdx-js/react": "^2.2.1",
+    "@next/mdx": "^13.1.1",
     "@tailwindcss/typography": "^0.5.8",
     "clsx": "^1.2.1",
-    "gray-matter": "^4.0.3",
     "next": "13.1.1",
     "react": "18.2.0",
-    "react-dom": "18.2.0",
-    "remark": "^14.0.2",
-    "remark-html": "^15.0.1"
+    "react-dom": "18.2.0"
   },
   "devDependencies": {
     "@babel/core": "^7.20.2",