Default value for visibilityTimeout in SqsStreamSettings should be set to None

[GuillaumeSaintRaymondSonos]

It's misleading because if visibilityTimeout is not overriden to None we can't use the value configured globally on the queue. And since it has a default value, it's easy to forget that this field has been set.

I think it will avoid some future suprises if visibilityTimeout is set to None → https://github.com/zio/zio-sqs/blob/master/src/main/scala/zio/sqs/SqsStreamSettings.scala#L9

Especially visibilityTimeout has a value of 30 which is the AWS default value so it doesn't provides much value.

The other default values are fine to me because they affect only the consumer behaviour.