Make the behaviour clear when providing a Service URI

[adammorr]

JustSaying allows you to provide a SerivceURI through the fluent API and DefaultAwsClientFactory which is then passed down to the underlying AWS SNS / SQS clients.

This is great for testing as it allows you to use libraries like LocalStack, however, there is a subtle behaviour change in that any region provided will be ignored by the AWS clients if a ServiceURI is provided and visa versa (see AWS client config).

To avoid consumers of JustSaying falling into this trap, we should look to surface this information in the public API somewhere so that it is clear what the behaviour is.

[yfesenko]

This was a really tricky and time consuming thing to be trapped by. Would be nice if it is better documented (or have the sample app(s) have comments to highlight this)