Custom client configuration NOT considered when using SQS

[ribeaud]

This issue relates to #63.
The PR only corrects SqsClientConfiguration.

[ribeaud]

As a workaround and to be able to use your own ClientConfiguration (with proxy settings for example), you might do the following:

• Do NOT use EnableSqs annotation and switch off the auto configuration for SQS:

@SpringBootApplication(exclude = MessagingAutoConfiguration.class)
class Application { ...

• But import SqsConfiguration:

@SpringBootApplication(exclude = MessagingAutoConfiguration.class)
@Import(SqsConfiguration.class)
class Application { ...

• And finally declare your own AmazonSQSAsync @Bean definition