Move next-bundle-analyzer to Next.js repo (#6445)

* Move next-bundle-analyzer to Next.js repo

* Remove options from bundle-analyzer

packages/next-bundle-analyzer/index.js

+module.exports = ({ enabled = true } = {}) => (nextConfig = {}) => {
+  return Object.assign({}, nextConfig, {
+    webpack (config, options) {
+      if (enabled) {
+        const { BundleAnalyzerPlugin } = require('webpack-bundle-analyzer')
+        config.plugins.push(
+          new BundleAnalyzerPlugin({
+            analyzerMode: 'static',
+            reportFilename: options.isServer ? '../analyze/server.html' : './analyze/client.html'
+          })
+        )
+      }
+
+      if (typeof nextConfig.webpack === 'function') {
+        return nextConfig.webpack(config, options)
+      }
+      return config
+    }
+  })
+}

packages/next-bundle-analyzer/package.json

+{
+  "name": "@next/bundle-analyzer",
+  "version": "0.0.1",
+  "main": "index.js",
+  "license": "MIT",
+  "repository": {
+    "url" : "zeit/next.js",
+    "directory": "packages/next-bundle-analyzer"
+  },
+  "dependencies": {
+    "webpack-bundle-analyzer": "3.0.3"
+  }
+}

packages/next-bundle-analyzer/readme.md

+# Next.js + Webpack Bundle Analyzer
+
+Use `webpack-bundle-analyzer` in your Next.js project
+
+## Installation
+
+```
+npm install --save @next/bundle-analyzer
+```
+
+or
+
+```
+yarn add @next/bundle-analyzer
+```
+
+### Usage with environment variables
+
+Create a next.config.js (and make sure you have next-bundle-analyzer set up)
+
+```js
+const withBundleAnalyzer = require("@next/bundle-analyzer")({ enabled: process.env.ANALYZE === "true" });
+module.exports = withBundleAnalyzer({});
+```
+
+Then you can run the command below:
+
+```bash
+# Analyze is done on build when env var is set
+ANALYZE=true yarn build
+```
+
+When enabled two HTML files (client.html and server.html) will be outputted to `<distDir>/analyze/`. One will be for the server bundle, one for the browser bundle.