Add compatibility with Android Gradle Plugin 8.0 #1353 (#1359)

* Adds a namespace for compatibility with AGP 8.0.

* Adds a android namespace for demo app

@@ -26,6 +26,7 @@ apply plugin: 'kotlin-android'
 apply from: "$flutterRoot/packages/flutter_tools/gradle/flutter.gradle"
 
 android {
+    namespace 'net.nfet.printing_demo'
     compileSdkVersion flutter.compileSdkVersion
     ndkVersion flutter.ndkVersion
 

@@ -22,6 +22,10 @@ rootProject.allprojects {
 apply plugin: 'com.android.library'
 
 android {
+    // Conditional for compatibility with AGP <4.2.
+    if (project.android.hasProperty("namespace")) {
+      namespace 'net.nfet.flutter.printing'
+    }
     compileSdkVersion 30
 
     compileOptions {