Gmail add-on: Add HTML Webpack plugin for AppsScript template

webpack_v3.config.js

const HtmlWebpackPlugin = require("html-webpack-plugin");

[...]
 module.exports = {
 [...]
  plugins: [
    new HtmlWebpackPlugin({
      filename: "appsscript.json",
      template: join(root, "config", "appsscript.json.ejs"),
      chunks: [],
      addon: {
        name: "My Gmail add-on"
      },
    }),
  ],
}