docs(v2): Docs refactoring and reorganization (#3831)

* stable refactor of plugins api documentation

* plugins sidebar not collapsed by default as small?

* theme docs reorg

* Refactor migration guide doc

* fix broken link

website/docs/api/plugins/plugin-google-analytics.md

@@ -0,0 +1,34 @@
+---
+id: plugin-google-analytics
+title: '📦 plugin-google-analytics'
+slug: '/api/plugins/@docusaurus/plugin-google-analytics'
+---
+
+The default [Google Analytics](https://developers.google.com/analytics/devguides/collection/analyticsjs/) plugin. It is a JavaScript library for measuring how users interact with your website.
+
+## Installation
+
+```bash npm2yarn
+npm install --save @docusaurus/plugin-google-analytics
+```
+
+:::tip
+
+If you have installed `@docusaurus/preset-classic`, you don't need to install it as a dependency.
+
+:::
+
+## Configuration
+
+```js title="docusaurus.config.js"
+module.exports = {
+  plugins: ['@docusaurus/plugin-google-analytics'],
+  themeConfig: {
+    googleAnalytics: {
+      trackingID: 'UA-141789564-1',
+      // Optional fields.
+      anonymizeIP: true, // Should IPs be anonymized?
+    },
+  },
+};
+```