title: Expo app.config.js googleServicesFile for different build variants
body: <p>I want to be able to differentiate between build variants on my Expo App.</p>
  <p>At the moment I have my expo config in my app.config.js like so</p>
  <pre class="lang-js prettyprint-override"><code>
  import Constants from 'expo-constants';
  
  let AndroidGoogleServicesFile = './google-services-dev.json';
  
  if (Constants.manifest.releaseChannel === 'staging') {
    AndroidGoogleServicesFile = './google-services-staging.json';
  }
  if (Constants.manifest.releaseChannel === 'release') {
    AndroidGoogleServicesFile = './google-services.json';
  }
  ...
  {
  ...
  android: {
    adaptiveIcon: {
      foregroundImage: './assets/images/adaptive-icon.png',
      backgroundColor: '#FFFFFF',
    },
    package: 'com.companyname.App',
    googleServicesFile: AndroidGoogleServicesFile,
  },
  ...
  </code></pre>
  <p>AS you can see i want to be able to configure my <code>googleServicesFile</code> based on <code>releaseChannel</code> or build variant but this doesn't seem possible at the moment? I am using EAS to build aswell and i'm not sure i can configure it in my <code>eas.json</code> either...</p>