title: Change "App Icon Source" in "Target > General" (not Info.plist) using (Fastlane-)script
body: <p>I just started using Fastlane for automatic deployment of our iOS apps. We have a few white labels (same app, different styling, content, icons, etc.). </p>
  
  <p>Using Fastlane I'm able to change almost all settings before starting the build (version &amp; build number, Launch Screen File, etc.).</p>
  
  <p>Where I'm struggling is the App Icon Source. We use image sets (one <code>AppIcon-NAME.appiconset</code> per app). See below image for reference where it's set:
  <a href="https://i.stack.imgur.com/Ai2ZV.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Ai2ZV.png" alt="enter image description here"></a></p>
  
  <p>How would I go about changing this property using Fastlane, any other custom script or in the build phase? This seems to be changes in <code>xcodeproj.pbxproj</code> and not <code>Info.plist</code>, which makes it significantly harder to find.</p>
  
  <p>Thanks.</p>