Refactor `DynamicMarkdown`

[mithi]

I've been copy pasting this everywhere. Put this somewhere to be reusable

import dynamic from "next/dynamic"
import { SpinnerDots } from "components/spinner"

const DynamicMarkdownRender = dynamic(() => import("components/markdown-render"), {
    // eslint-disable-next-line react/display-name
    loading: () => <SpinnerDots />,
})

They're found in the following:

• theme-menu.js
• content/react/advanced-hooks/3
• content/landing
• pages/react/[section]