Constructs AmazonSimpleNotificationServiceClient with the credentials loaded from the application's default configuration, and if unsuccessful from the Instance Profile service on an EC2 instance. Example App.config with credentials set.

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<?xml version="1.0" encoding="utf-8" ?>
<configuration>
    <appSettings>
        <add key="AWSAccessKey" value="********************"/>
        <add key="AWSSecretKey" value="****************************************"/>
    </appSettings>
</configuration>

public AmazonSimpleNotificationServiceClient(
	AmazonSimpleNotificationServiceConfig config
)