Implemented structure for push Notifications

android/app/src/main/java/io/flutter/app/FlutterMultiDexApplication.java

@@ -0,0 +1,25 @@
+// Generated file.
+//
+// If you wish to remove Flutter's multidex support, delete this entire file.
+//
+// Modifications to this file should be done in a copy under a different name
+// as this file may be regenerated.
+
+package io.flutter.app;
+
+import android.app.Application;
+import android.content.Context;
+import androidx.annotation.CallSuper;
+import androidx.multidex.MultiDex;
+
+/**
+ * Extension of {@link android.app.Application}, adding multidex support.
+ */
+public class FlutterMultiDexApplication extends Application {
+  @Override
+  @CallSuper
+  protected void attachBaseContext(Context base) {
+    super.attachBaseContext(base);
+    MultiDex.install(this);
+  }
+}