Merge pull request aws-amplify#1 from thanhminhkma/fix/background_android_cancel

[CancelOperation] config run on background

Author: metajet98

packages/amplify_api/android/src/main/kotlin/com/amazonaws/amplify/amplify_api/AmplifyApiPlugin.kt

@@ -16,6 +16,7 @@
 package com.amazonaws.amplify.amplify_api
 
 import android.content.Context
+import android.os.AsyncTask
 import android.os.Handler
 import android.os.Looper
 import androidx.annotation.NonNull
@@ -132,8 +133,12 @@ class AmplifyApiPlugin : FlutterPlugin, MethodCallHandler {
         cancelToken: String
     ) {
         if (OperationsManager.containsOperation(cancelToken)) {
-            OperationsManager.cancelOperation(cancelToken)
-            flutterResult.success("Operation Canceled")
+            AsyncTask.execute {
+                OperationsManager.cancelOperation(cancelToken)
+                handler.post {
+                    flutterResult.success("Operation Canceled")
+                }
+            }
         } else {
             flutterResult.error(
                 "AmplifyAPI-CancelError",