title: Ionic 5 : How to setup custom webpack config?
body: <p><br></p>
  
  <p>I am trying to setup a custom webpack config to my ionic 5 app,
  there is nothing about that in ionic 5 documentation, so I followed ionic 3 doc.</p>
  
  <p>In my package.json I add script and config like this: </p>
  
  <pre><code> "scripts": {
      "ng": "ng",
      "start": "ng serve",
      "build": "ng build",
      "test": "ng test",
      "lint": "ng lint",
      "e2e": "ng e2e",
      "build:apk": "ionic cordova build android",
      "ionic:serve": "ionic-app-scripts serve"
    },
    "private": true,
    "config": {
      "ionic_webpack": "custom.webpack.config.js"
    },
  </code></pre>
  
  <p>when I run "ionic serve" I got this error: </p>
  
  <pre><code>src\app\main.ts was not found. The "main.dev.ts" and "main.prod.ts"
  [npm]             files have been deprecated. Please create a new file "main.ts" containing the content of "main.dev.ts", and
  </code></pre>
  
  <p>I would to know if there is a different way in ionic 5, or something else helpful</p>