ANR from `AndroidMqttClient` during MQTT initialization

[alvarisi]

Hi
@deepanshu42 @alfianlosari
we found that the initialization causing an ANR, we record them using ANR Watchdog with below stacktrace.

com.github.anrwatchdog.ANRError: Application Not Responding for at least 5000 ms.
Caused by: com.github.anrwatchdog.ANRError$$$_Thread: main (state = RUNNABLE)
at com.gojek.mqtt.client.v3.impl.AndroidMqttClient.<init>(AndroidMqttClient.kt:179)
at com.gojek.mqtt.client.v3.impl.AndroidMqttClient.<init>(AndroidMqttClient.kt:80)
at com.gojek.mqtt.client.factory.AndroidMqttClientFactory.createAndroidMqttClient(IAndroidMqttClientFactory.kt:49)
at com.gojek.mqtt.client.internal.MqttClientInternal.<init>(MqttClientInternal.kt:65)
at com.gojek.mqtt.client.factory.MqttClientFactory$Companion.create(MqttClientFactory.kt:15)
at com.gojek.courier.courier_dart_sdk.internal.MqttClientDelegate.<init>(MqttClientDelegate.kt:15)
at com.gojek.courier.courier_dart_sdk.CourierDartSdkPlugin.initialise(CourierDartSdkPlugin.kt:141)
at com.gojek.courier.courier_dart_sdk.CourierDartSdkPlugin.onMethodCall(CourierDartSdkPlugin.kt:65)
at io.flutter.plugin.common.MethodChannel$IncomingMethodCallHandler.onMessage(MethodChannel.java:267)
at io.flutter.embedding.engine.dart.DartMessenger.invokeHandler(DartMessenger.java:292)
at io.flutter.embedding.engine.dart.DartMessenger.lambda$dispatchMessageToQueue$0$io-flutter-embedding-engine-dart-DartMessenger(DartMessenger.java:319)
at io.flutter.embedding.engine.dart.DartMessenger$$ExternalSyntheticLambda0.run(Unknown Source:12)
at android.os.Handler.handleCallback(Handler.java:959)
at android.os.Handler.dispatchMessage(Handler.java:100)
at android.os.Looper.loopOnce(Looper.java:257)
at android.os.Looper.loop(Looper.java:342)
at android.app.ActivityThread.main(ActivityThread.java:9638)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:619)

Hence as part from the fix we are raising an MR for running them in background thread as quick fix.