Add prefix to application id during debug

This allows to install the application side by side on a real device where the
production app is installed as well

android/app/build.gradle

@@ -99,6 +99,9 @@ android {
             // Signing with the debug keys for now, so `flutter run --release` works.
             signingConfig signingConfigs.release
         }
+        debug {
+            applicationIdSuffix ".debug"
+        }
     }
 }