title: Use custom name for android module in flutter project
body: <p>I have an existing Android project.
  Also, I created a new flutter project. I copied my project to it. Now I have such tree in the file system:</p>
  
  <pre><code>my_flutter_project/
      android/
          my_android_module_name/
             src/...
      lib/...
      ios/...
  </code></pre>
  
  <p>When I try to run flutter project I have such error:</p>
  
  <pre><code>No application found for TargetPlatform.android_arm64.
  Is your project missing an android/app/src/main/AndroidManifest.xml?
  </code></pre>
  
  <p>So I should somewhere write <code>my_android_module_name</code> instead <code>app</code> but where?</p>